Fossil Field Trip Manitou Formation
Jerry Suchan (email@example.com)
Revision 7, 11 May 2004
If you want to see what was found on this field trip, use this link: Field Trip Results and Photographs of Specimens.
(Linked from )
The following is information for the joint Western Interior Paleontological Society (WIPS) ( http://www.wipsppc.com/ ) and Colorado Springs Mineralogical Society (CSMS) fossil field trip, to be held Sunday 2 May 2004.
References in this article are numbers inside brackets [xx], with the actual references located at the end of this article. I would have like to have linked some of the web based pictures referenced directly to this article, but that would make this page load too slowly. So go to the reference and look for yourself.
I would like to invite the Amateur (as well as professional) Paleontological community to work together and broaden our mutual knowledge. If anyone else has anything to contribute, like specimen photos I can link in, or more identifications or references, please do contact me.
*** *** *** Contents *** *** ***
Field Trip Information
Field Trip Etiquette and Required Forms
Geology and Paleontology of the Manitou Formation
Stratographic column of the Paleozoic in the Colorado Springs Area
The Manitou Formation
The Peerless Formation
Life of the Ordovician
Depiction of "typical" Ordovician Life
Specimen 1. Trilobite, species 1
Specimen 2. Trilobite, probably same species as species 1
Specimen 3. Curled trilobite, Leiostegium sp.
Specimen 4. Giant trilobite, Kainella sp.
Specimen 5. Cystoid plate
Specimen 6. Cystoid stalk
Cystoid illustrating how the calyx is made up of several plates
Specimen 7. Brachiopod, Brachiopod, Apheoorthis linecosta
Specimen 8. Brachiopod, Lingulata, sp.
Specimen 9. Trace fossils
Specimen 10. Stromatolite
*** *** *** *** *** ***
Field Trip Information
To study the Manitou (Ordovician) and associated formations and to collect
samples of associated fossils.
Date: Sunday 2 May 2004
Assembly time: 8:30 to 9:00 am. At 9:00 am we leave and any late comers are on their own, but can probably find us using
the maps provided below.
Assembly location: Deckers Colorado, at the intersection of SH 67 and 126. Any changes in this will be provided as required.
Field trip leader: Jerry Suchan
9603 Woodcliff Ct.
Peyton CO, 80831
How long will we stay? Until the last member is ready to leave.
Cancellation: The trip will be called in case of rain or snow or in general weather bad enough to prevent pleasant outdoor activity. Feel free to call the trip leader (that's me) to check on cancellation, but I will leave home by 6 am and if you call after that and get no answer the trip is not canceled.
We will be studying the geology of this region and specifically looking for marine fossils in the Manitou Formation. You will need the following equipment and supplies:
Another good web site showing this location and some fossils found there is WIPS member Steve Wagner's PALEOCURRENTS: Trilobite collecting in Colorado Rockies.
Field Trip Etiquette and Required Forms
Please respect the fossils.
Activities of the field trip members will be governed by the goals and missions of the respective sponsoring societies, the Western Interior Paleontological Society (WIPS) and the Colorado Springs Mineralogical Society (CSMS). I am a member of both of these amateur earth science clubs. I also ask field trip members to follow the Field Trip Leader's Guidelines as provided below.
Members of WIPS are asked to sign the two page Release of Liability form at the beginning of the field trip. You can streamline the paperwork by downloading copies of them HERE, print them out, then sign and bring them to the Field Trip with you.
CSMS uses the Rocky Mountain Federation of Mineralogical Societies release on all official field trips. Roger Pittman, CSMS Field Trip Director will either come on this trip or make sure that releases are available. When CSMS members have signed the RMFMS release they are covered with the RMFMS liability insurance policy.
All field trip participants are asked to sign a field trip log, providing their name, address, phone number, and club affiliation.
Mission of the Western Interior Paleontological Society:
The purposes of the Society shall be scientific, educational, and charitable and shall include field trips, lectures, seminars and other educational and science-related activities; the making available of information as to exploring for, identifying, preparing, preserving, and displaying fossils; encouraging adherence to responsible codes of conduct in the exploration for and collection of fossils; assisting museums and educational institutions in the furtherance of their paleontology-related activities; and cooperating with government authorities in the development of laws governing the collection of fossils and their preservation for future generations.
Colorado Springs Mineralogical Society is an incorporated, non profit organization with these goals:
Field Trip Leader's Guidelines:
Geology and Paleontology of the Manitou Formation
The Manitou Formation, also called Manitou Dolomites, is a marine (ocean) deposit, Ordovician in age, which is exposed along the Front Range of Colorado, and extending both south (as far as the San Luis Valley), and north and west (as far as northern Sangre De Cristo range in the San Isabel National Forest of south central Colorado) from there.
Formations exposed in this area are the Sawatch (maybe), Peerless, Manitou and nearby the Fountain, as well as various forms of granite. All except the granite are all Paleozoic deposits, and their relationships are depicted in the following generalized Stratographic column. (Geologic dates in this article may vary somewhat depending on the source they were obtained from.)
Stratographic column of the Paleozoic in the Colorado Springs Area.
Paleozoic Permian Lyons Formation Pennsylvanian
(310 million to 280 million years ago)
Fountain Formation Mississippian Williams Canyon Fm
Devonian (no evidence of deposition) Silurian (no evidence of deposition) Ordovician
(500 million to 439 million years ago)
(600 million to 500 million years ago)
We will concentrate on the Manitou Formation because it is the one with the interesting fossils. However I touch on the Peerless formation also because in Manitou Park it contacts the lower part of the Manitou, and is also described as being similar in appearance and contains some fossils. Discussion and understanding of geologic formations can be a challenge. I provide below a description of these two formations for our consideration on this field trip.
The Manitou Formation  --- First described by Cross  (1894, p2.) and named for exposures at Manitou park and Manitou Springs in the Manitou Springs Quadrangle. Findley (1916) assigned an Ordocian age to the formation on the basis of fossils and stratigraphic position. Brainerd, Baldwin, and Keyte  (1933, p.380) formally designated the section in Williams Canyon on the northern outskirts of Manitou Springs as the type for the Manitou Limestone. The Manitou formation consists of finely to coarsely crystalline limestone and minor amounts of dolomite at its type location. In Manitou park the formation consists chiefly of dense red dolomite as in the vicinity of Missouri Gulch, and trilobites occur mainly in thin beds of limestone.
The Peerless Formation  --- In 1932 Behre proposed that the term Peerless shale member be applied to the upper part of the Peerless Quartzite in the Western Mining district north of Leadville. Tweto (1949) followed Singelwald (1947) in considered the unit a separate formation, "easily distinguished from the Sawatch quartzite in an extensive area northwest of Leadville." In the Pando area north of Leadville (in the Holy Cross area, between Leadville and I70) the Peerless Formation "comprises about 100 feet of dolomitic sandstone, sandy dolomitic shale, and dolomite which weathers dark brown or brownish maroon. The dolomitic rocks are buff, tan, green, pink, and maroon, and many of them are mottled in various combinations of these colors. The lower portion of the Peerless formation in the Pando area contain strata similar to those between the Sawatch quartzite and Manitou formation in Illinois and Missouri Gulches. Few fossils have been collected from the Sawatch quartzite and the Peerless formations and their ages have never been certain within the Cambrian.
Well anyway, what this mostly tells us is that in Manotu Park, if we find Trilobites, or indeed if there are abundant fossil body parts of any kind, the we are most likely collecting in the Manitou Formation. A fun geological puzzle is to identify the various formations in the field.
The Manitou Formation exposed at the field trip area is a red dolomite. Dolomite (CaMg(CO3)2) is a magnesia-rich sedimentary rock resembling limestone (CaCO3). In its pure form it is a white or light-colored mineral, used in fertilizer, as a furnace refractory, and as a construction and ceramic material. Dolomite is harder and more resistant to weathering than limestone. It is also harder to split with hammers and chiseled, so be prepared with appropriate equipment as I outlined above.
I do not have a complete explanation of the red color of this marine sediment of the Manitou Formation. It is probable that some form of iron, such as limonite, is the source of the color. Limonite is "any of a group of widely occurring yellowish- brown to black iron oxide minerals, essentially FeO(OH)ĚnH2O, used as a minor ore of iron." Think of limonite as a kind if natural rust. Often geologic deposits are a deep red or even purple color related to small limonite or other iron mineral inclusions. When these colors are in layers, especially also with other colors of any kind like browns and greens, they are referred to as variegated. For terrestrial deposits this is often interpreted as representing a dryer climate or a situation where there was not much moisture in the soil at the time it was deposited, such as dried flood plains, or even desert conditions. Clearly this explanation does not apply to marine formations, as they are marine not terrestrial and a more or less solid reddish color.
Fossils are commonly collected from this location using hammers and chisels and even pry bars to split the rocks and expose the specimens. I have also found very good specimens where they were weathered and exposed on the surface of undisturbed material. This location has been collected for some time by both amateurs and professionals, and such weathered exposures and not common. It may also be possible to simulate this natural weathering by etching the specimens into low profile exposures on slabs of fossiliferous slabs of limonite.
With some interesting trilobite exception, the fossils of this formation are all quite small, say the size of a finger nail and smaller yet. You will want to bring a good magnifying lens to assist with your collecting. If you are only looking for hand size or large and showy specimens you may well be disappointed with this location.
The paleontology of the Manitou Formation is more or less representative of the Ordovician Period, as described below.
Life of the Ordovician
The following information can be found in  and .
of "typical" Ordovician Life.
(Linked from )
The Ordovician period began approximately 510 million years ago, with the end of the Cambrian, and ended around 445 million years ago, with the beginning of the Silurian. At this time, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern super-continent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater.
Ordovician marine strata are characterized by numerous and diverse trilobites, graptolites and conodonts (phosphatic fossils with a tooth-like appearance), algae and sponges. In addition, blastoids, bryozoans, corals, crinoids, as well as many kinds of brachiopods, snails, clams, and cephalopods appeared for the first time in the geologic record in tropical Ordovician environments. Remains of jawless, armored fish (informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi) from Ordovician rocks comprise some of the oldest vertebrate fossils.
I have found many of these fossils in the Manitou Formation. Conodonts and ostraderms, along with other fossils can be found in the Harding Formation, outcrops of which are accessible elsewhere in Colorado. The Harding Formation is a candidate for a future field trip. I suspect that there are conodonts in the Manitou Formation, but these are micro fossils which require special collecting and preparation techniques. As there are some members of WIPS which specialize in microfossils, I am hopeful that evidence of conodonts can be obtained on this field trip.
Perhaps the most eventful occurrence of the Ordovician was the colonization of the land. Remains of early terrestrial arthropods are known from this time, as are microssils of the cells, cuticle, and spores of early land plants. Of course, as the Manitou Formation is marine we will not expect to find evidence of these land fossils, and which would be very difficult to observe in any case.
From the Early to Middle Ordovician, the earth experienced a milder climate in which the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Late Ordovician, massive glaciers formed causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician, in which 60% of all marine invertebrate genera and 25% of all families went extinct. (What, no meteor crater?)
Before you get too deep into these pictures, there is just one warning, These are the best of all the specimens I have seen and photographed over the last 20 years. Some are my specimens and some belong to others. If we find even one trilobite specimen during the field trip which is as good as those illustrated here, I will be surprised. You will find some specimens, but the great ones are few and far between.
Please respect the fossils.
Putting this article together and adding pictures of the specimens has provided me with a wonderful opportunity to digitize my old slides. These slides are pictures of specimens found in prior field trips to this location. My main focus with fossils, after I find, them it to document their existence with photographs. I have a fairly interesting database of pictures of fossils found in Colorado which I will make available to anyone at my cost. Likewise, anyone wanting the full set of digital pictures of specimens from just these locations can have them at my cost. Also, I am interested in photographing other people's specimens in order to add them to this database.
In most cases I have not identified the specimens, even to the genus. This provides a wonderful opportunity for interested people to work on the identification of these and other specimens. If anyone is interested, please contact me, as I would be interested in collaborating with an identification effort. Reference  is an excellent trilobite starting point for such a project.
Trilobite's reported in  from the Manitou Park are as follows:
Illinois Gulch. Exposures of the Peerless formation along the trail. (As was pointed out in the discussion above, few fossils have been collected from this formation.)
Ellipsocephaloides butler Resser
Idahoia wisconsensis (Owen)
Ptychaspis granulusa (Owen)
Missouri Gulch. Quarry in the Manitou formation. (This formation is where we will find most of the fossils. Interestingly, there are five genera of trilobites listed here.)
Leiostegium (Leoistegium) manituensis Walcott
Hystricurus? aff. H.? genacurus (Hintze)
Bellefontia cf. B. chamberlaini Clark
Symphysurina cf. S. globocapitella Hintze
Specimen 1. (below,
species 1. About an inch across. This specimen is missing it's head (aka
Specimen 2. (below, right) Trilobite, also species 1, but has fully preserved spines. Very long spines, in fact. This specimen is also missing it's cephalon. Interestingly, there is nothing like this illustrated in . Scale is 1 inch.
Trilobite specialists call the head of the trilobite the "cephalon", and call the tail or posterior region of the trilobite the "pygidium". You can find all the names and labels associated with trilobites in  and . Trilobites have been extinct for a long time, but if you were to meet one you probably wouldn't like it. A trilobite is really most like a bug with lots of feet.
(Walking trilobite, linked from .)
Specimen 3. (below) Curled trilobite, Leiostegium sp. Scale is 1 inch. Most trilobite specimens are more or less flat, but this one is somewhat curled. This is the trilobite species most commonly found at this location. Oscar (Turk) Price specimen.
Identification of this specimen as genus Leiostegium is somewhat tentative. Certainly this specimen bears a close resemblance to the illustrations of the various species of Leiostegium in . Amongst the genera and subgenera of Genus Leiostegium Raymond, 1913 listed there are: Subgenus Leiostegium Manitouensis Walcott, 1925; Subgenus Leiostegium Perischodiry Raymond, 1937, Leiostegium (Leiostegium) sp., Leiostegium (Perischodory) Incomoertum new sp.; Subgenus Manitouella new subgenera, Leiostegium (Manitouella) Ulrici, new sp. There are 14 different figures illustrating these, all of which are only heads (cephalons) or tails (pygidiums), with not complete body fossil, and all appearing quite similar. To definitively make any distinctions I am of the opinion that comparison to the real specimens illustrated, not pictures of them, is required. In any case, the comment that the Leiostegium Manitouensis "is abundantly represented in the Manitou formation, but it's preservation in most cases leaves much to be desired" is revealing. The authors of  did not find the differentiation of these species to be an easy task. Still cephalons and pygidiums similar to specimen 3 are common in this location.
Specimen 4. (below) Giant Trilobite, Kainella sp. Two pictures. The actual fossil is a giant trilobite head part (cephalon anterior border). Scale on the left is 1 inch. On the right is a model of a whole trilobite (not the same species as the fossil) with the model head compared to the fossil provides an idea of how large the live animal was. This is an example of an unusually large large trilobite from this location.
This specimen correlates in , on p. 117, with: Genus Kainella, Walcott, 1925; Kainella sp. cf. K. Billingsi Walcott Pl. 21, fig. 6, 13; Kainelli billingsi Walcott, 1925, p. 102, pl. 22, figs. 1-7. In this paper it is said that, "An enormous cranidium is illustrated (pl. 22, fig 13) without assurance that it belongs to this species. It is the largest known for the genus."
Genus Kainella is also described in Index Fossils of North, America  on p. 647-8 and Kainella billingsi (Walcott) Plate 274 - 9.
 places the genus Kainella in Order Asaphida, Superfamily Remopleuridoidea.
Bear in mind that there are a lot of trilobites that have been named. For example, according to , "There are over 180 families of trilobites, and about 5000 genera, which contain the 15,000+ described species of trilobites!"
Why are all these specimens except one missing their cephalon or are just pieces? Trilobites are arthropods (meaning joint legged) and as such have chitinous exoskeletons, just like insects and crabs. When the animal outgrows its exoskeleton it splits the exoskeleton open and climbs out. Then it solidifies a new exoskeleton over it's now somewhat larger body. This leaves the parts of the exoskeleton lying about and so provides lots of fossils for amateur and professional paleontologists to study. The down side is the specimens are incomplete pieces. Sometimes the animal dies and then there is the opportunity for a whole exoskeleton to be preserved, as is illustrated by Specimen 3.
More modern arthropods, such as crabs, have learned a survival technique that trilobites did not use. They recycle. These modern animals eat their shed exoskeleton and so are able to use the chitin for food and energy, which then can then contribute to regrowing their new exoskeleton. Of course, this is a loss for the paleontologist, because then there are a lot fewer pieces of the shed exoskeleton lying around to be fossilized.
Specimen 5. (below,
left). Cystoid plate. This is actually the mold rather than the plate itself. Scale is 0.1 inch.
Specimen 6. (below, right). Cystoid stalk (read more below). I interpret this to be a Cystoid stalk rather than a Crinoid stalk because I have not found crinoids at this location, and of course these are found in general association with the Cistoid plates. Scale is 0.1 inch.
Nope, they aren't very large fossils. Bring your magnifying lens.
Through revision 2 of this article I interpreted these as Blastoid fossils. However, after discussing these specimens with WIPS member Steve Wagner, further investigation revealed that Blastoids and Crinoids display certain 5 fold symmetry, whereas Cystoids can display either, or none, depending on the species.
Cystoid (Lepadocystit decorus, found in Larson Quarry in Sycamore, Illinois)
This illustrates how the calyx is made up of several plates. Age of this specimen not provided.
(linked from )
References , , and  were used to provide the following description: Class Cystoidae are stemmed or stem-less echinoderms (includes echinoderms, star fish, sea urchins, blastoids, sea cucumbers) with a globular or pear shaped test (aka hard external covering, aka calyx, aka theka) composed of a variable number of calcareous plates (thirteen to several hundred) arranged with or without symmetry. They are extinct marine invertebrates which flourished only during Paleozoic times.
For a comparison of cystoids to blastoids, from  the Blastoidea is an extinct taxon of echinoderms. Originating in the Ordovician along with many other echinoderm classes, they reached their greatest diversity in the Mississippian, or early Carboniferous, and persisted until the end of Permian. Like most echinoderms, blastoids were protected by a set of interlocking plates of calcium carbonate, forming the theca. Blastoids show a very regular and tightly integrated plate arrangement, which is in part responsible for their abundance as fossils: the theca held together after the animal died. In life, the theca of a typical blastoid was attached to a stalk, or column, made up of stacked disc-shaped plates. The other end of the column attached to the ocean floor -- very much like stalked crinoids.
Specimen 7. (below, left)
Brachiopod, Apheoorthis linecosta (Walcott). Scale is 0.1 inch.
Specimen 8. (below, right) Brachiopod, genus Lingulata. Scale is 0.1 inch.
Nope, they aren't very large fossils either.
Concerning the identification of Specimen 7, Mr. Jack Null sent me the following information on the first day this article was published: "... the more common brachiopod at Illinois Gulch, and which you have added in your photo display, is called Apheoorthis linecosta (Walcott). Shimer and Schrock  [Index Fossils of North America] have it pictured on plate 110, #34-37." Great work Jack! This is an example of how the amateur Peolontological community can work together and broaden our mutual knowledge. If anyone else has anything to contribute, like specimen photos I can link in, or more identifications or references, please do contact me.
As described in , Brachiopods are marine animals that, upon first glance, look like clams. They are actually quite different from clams in their anatomy, and they are not closely related to the molluscs. They are lophophorates, and so are related to the Bryozoa and Phoronida.
You can usually distinguish between brachiopods and clams (aka bivalves, aka pelecypods) in that each shell (aka valve) of a brachiopod is bilaterally symmetrical (the right side and left side are mirror images of each other), while at the same time the two valves are dissimilar.  provides a good explanation of this and other Brachiopod morphology and ecology. In comparison, a single valve of a clam may not be bilaterally symmetrical, but usually the two valves are mirror images of each other.
Specimen 9. (below) Trace fossils. The long, thin, straight marks as well as the wide "U" shaped band at the top of the specimen are trace fossils. These particular ones are probably produced by animals (usually said to be "worms") burrowing through the mud of the ancient Ordovician sea bottom. So far I haven't found any trilobite foot prints, but those aren't very common since they probably swam around rather than walked.
As described in , trace fossils, or ichnofossils, are the evidence of bioturbation preserved in sediments, produced in soft sediments and hard substrates as a result of the living activities of organisms. They include surface tracks and trails, subsurface burrows and borings, as well as fecal material and the marks produced by dying animals.
Specimen 10. (below) Stromatolite, produced by algae or bacteria. The fossil is the concentric rings of red and white in the picture. The rings are bout two inches in diameter. These are the only "plant" fossils we are likely to find at this location. They are not common there.
The definition of stromatolite provided by  is "A widely distributed sedimentary structure consisting of laminated carbonate or silicate rocks, produced over geologic time by the trapping, binding, or precipitating of sediment by groups of microorganisms, primarily cyanobacteria (aka blue-green algae)."
There are other definitions. For example  defines stromatolite as 'The most common usage is: a laminated, relief-forming structure of biogenic, specifically microbial, origin. Usually they are found in carbonate sediments, particularly Precambrian sediments. It is usually very difficult to demonstrate a biological origin, and care should be taken not to assume a biological origin for all "laminated, relief-forming structures" in carbonates.'
I have found that in practice that "stromatolite" is often used to refer to any sort of ringed and or layered structure preserved in the fossil record and which could be interpreted as being formed by layers of algal or bacteria activity. In general, demonstrating that a particular specimen, such as the one above, has a biological origin is not something that can usually be accomplished in the field with a hand lens. Certainly stromatolites are not restricted to the paleozoic, since stromatolites still grow today , though not abundantly.
Those of you who accompanied me in either of the past two years on the Wamsutter WIPS field trip had the opportunity to observe quite large stromatolites and entire stromatolitic reefs preserved at the base of the Green River formation, which is Eocene in age.
Internet references are not static. I maintain a copy of each of the following web references.
Ridgewood History, http://www.chucksphar.com/ridgewood/Stories/ridgewood_history.htm
Yahoo Maps, Location of Deckers, CO
TopoZone, topo map of field trip
Trilobites from the Perless and Manitou Formations of Colorado, Robert R. Berg and Reuben Ross Jr., Journal of Paleontology, v.33, No.1, p. 106-119, January 1959.
Cross, C.W., 1894, Description of the Pikes Peak Sheet, Colorado: U.S. Geological Survey, Geologic Atlas, Pikes Peak Folio No. 7, 5 p., maps
Brainerd, E.A., Baldwin, H.L., Jr., and Keyte I.A., 1933, Pre-Pennsylvanian Stratigraphy of Front Range in Colorado; Bull. Am. Ass. Petroleum Geologists, v. 17, p. 375-396
The Ordovician, 490 to 443 Million Years Ago, http://www.ucmp.berkeley.edu/ordovician/ordovician.html
Life of the Ordovician, http://www.ucmp.berkeley.edu/ordovician/ordolife.html
Introduction to the Blastoidea, http://www.ucmp.berkeley.edu/echinodermata/blastoidea.html
Introduction to the Brachiopoda, http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html
Definition: Bioturbation / Trace Fossils / Ichnotaxa, http://www.peripatus.gen.nz/Paleontology/defTraFos.html
Earth is a living museum, http://www-ecpm.u-strasbg.fr/Actu/A-curious/a-c-stromato.html
ALPHABETICAL LISTING OF TRILOBITE GENERIC NAMES, http://www.aloha.net/~smgon/genera.htm
Trilobite Glossary, http://www.es.mq.edu.au/MUCEP/trilobites/glossary.htm
Major Trilobite Features, http://www.aloha.net/~smgon/trilomajor.htm
BRACHIOPODA MORPHOLOGY AND ECOLOGY, http://paleo.cortland.edu/tutorial/Brachiopods/brachmorph.htm
Shimer, Hervey Woodbyrn and Shrock, Robert Rakes, "Index Fossils of North, America", published by The Massachusetts Institute of Technology, original copyright 1944, Multiple printings, I have the twelfth printing, July 1983, ISBN 0 262 19001 X
PICTORIAL GUIDE TO THE ORDER ASAPHIDA, http://www.aloha.net/~smgon/remopleuridoideaguide.htm
Lepadocystit decorus, cystoid described were found in Larson Quarry in Sycamore, Illinois, http://www.esconi.org/Dave%20Carlson-Congrat.htm
The Audubon Society Field Guide to North American, by Ida Thompson, First Printing, Library of Congress Catalog Number 81-84772
Invertebrate Paleontology, by William H. Twenhofel and Robert R. Shrock, First Edition, 1935