534 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Of crinoids, Weller 153 has determined that the following genera of 

 northwestern Europe are also present in the Chicago area (northern Illi- 

 nois, southeastern Wisconsin, and Iowa), but not elsewhere in the United 

 States: Botryocrinus (1 species), Corymb ocrinus (2), Crotalocrinus (1), 

 Marsupiocrinus (1), Melocrinus (1), Petalocrinus (2), and Pycnosaccus 

 (1). As crinoids are very sensitive to environment and change, rather 

 rapidly, this list is proof of direct migration from Europe. Further, in 

 the same area occur other genera that are found elsewhere in the United 

 States. These are: Callicrinus (New York and Tennessee), Eucalypto- 

 crinus (widely distributed), Gazacrinus (widely distributed), IcMliyo- 

 crinus (New York), Lecanocrinus (widely distributed), Lyriocrinus 

 (widely distributed), M y el o dactyl us (New York and Tennessee ),Periecho- 

 crinus (New York and Tennessee), and Thysanocrinus (New York and 

 Tennessee). But few of the species are common to two areas. In other 

 words, the majority of these crinoids are of one province — that of the 

 Hudson sea and the Arctic realm. The genera comprising the second lot 

 are more widely distributed, geologically and geographically, and are com- 

 mon to the Arctic and Atlantic realms. 



The crinoid genera of the New York basin are also common to the area 

 west of the Cincinnati axis and south of central Indiana — that is, the 

 Indiana basin. These are: Calceocrinus (not in the Chicago area), Calli- 

 crinus, Eucalypt ocrinus (a few species are common to the two areas),. 

 Euchir ocrinus (not in the Chicago area), Gazacrinus, Homocrinus (not 

 in the Chicago area), I chthy ocrinus, Lecanocrinus, Lyriocrinus, Macro- 

 stylocrinus (widely distributed in America), Mariacrinus (not in the 

 Chicago area), Myelodactylus, Periechocrinus, Pisocrinus (not in the 

 Chicago area), Stephanocrinus, and Thysanocrinus. In other words, 

 these crinoids are of one province — that of the Mississippian sea — and 

 belong directly to the Atlantic realm. Further, 5 genera of the Missis- 

 sippian province do not occur in the Hudson province, and 7 genera of 

 the latter area are unknown in the southern region. 



At present the corals of the Siluric have little stratigraphic value. 

 They begin to be common in the Rochester, from thence up to the Guelph 

 reefs occurring at different horizons, and judging from published lists 

 are about the same throughout. This is especially true of the Mississip- 

 pian and Hudson seas. Corals are never abundant in the Saint Lawrence 

 sea except on Anticosti, where the small reefs appear earlier than any of 

 those in the Mississippian sea. These forms are now being determined at 

 Yale. 



138 Weller : Bull. Chicago Academy of Sciences, vol. 4, 1900, pp. 1-153. 



