his laboratory for a discussion of the systematic relationships among 

 the South American chelyid turtles. Dr. Zangerl also collaborated 

 with Dr. Robert Sloan, of the Department of Geology of the Univer- 

 sity of Minnesota, in the study of the second known specimen of a 

 fossil sea- turtle, Desmatochelys lowi Williston (see page 58). 



Curator Richardson investigated an exposure of Upper Creta- 

 ceous Bearpaw shale on the shore of the Fort Peck Reservoir in 

 northern Montana to determine whether a paleoecological investi- 

 gation of that area on the model of the Mecca project would be feas- 

 ible (see page 34). Although he found abundant fossil ammonites 

 and lobsters, he found that the depositional environment was such 

 that a study of the proposed sort would not yield the desired infor- 

 mation. On his way back to Chicago he collected fossil vertebrates 

 near Fairburn, South Dakota. During the year he described a new 

 species of a large Pennsylvanian arthropod, Arthropleura, basing his 

 study on a specimen collected and presented to the Museum by Dr. 

 Glenn Boas, of Chicago (see below). 



Accessions— Geology 



A notable addition to the fossil invertebrate collection during the 

 year was a gift from Dr. Glenn Boas, of Chicago — the first piece of 

 the dorsal covering of an Arthropleura to be found in North America. 

 Arthropleura, the largest swamp-dwelling invertebrate, was a five- 

 foot-long monster resembling a myriapod or a sowbug but most 

 closely related to the trilobites. Dr. Boas collected the specimen in 

 the strip-mine dumps near Coal City, Illinois. Specimens of partial 

 legs were collected in 1952 by a Museum field party, and a complete 

 leg was found in 1953 by Mrs. John McLuckie of Coal City. Thus 

 the presence of Arthropleura in this deposit was known, but until the 

 specimen collected by Dr. Boas became available it had not been 

 possible to describe the species because the necessary characters for 

 comparison with known European species lie in the dorsal covering. 

 A very fine addition to the collection of fossil fishes is the large, 

 perfectly preserved Pennsylvanian shark excavated at the site of the 

 Museum's Logan Quarry in Parke County, Indiana (see page 55), 

 by Curators Richardson and Zangerl with the able assistance of Chief 

 Preparator Gilpin and Preparator Erickson. This specimen, of which 

 the tail had been removed by erosion long before the fossil was found, 

 has a length of 83^ feet from the tip of the head to a point just in 

 front of the pelvic girdle. The entire animal was probably 13 feet 

 long. In addition to this unique specimen, the Logan Quarry has 



56 



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