THE FOSSIL rRTNOTD GENUS DOLATOCRLNllS AND ITS ALLIES. 



By Frank Springer. 



Associate in Paleontology, United States National Museum. 



CRINOID FAUNAS 0I<^ THE MIDDLE DEVONIAN. 



The crinoids which form the subject of this Bulletin constitute a 

 small group of generic forms having a singularly restricted distribu- 

 tion, being confined, so far as known (after a feeble beginning with 

 two hitherto undescribed species in the Niagaran and Helderber- 

 gian)/ to the Middle Devonian of North America. They belong 

 typically to the Gulf fauna, which during Onondaga time brought 

 widespread coral reefs into the interior region — best developed in the 

 Louisville, Kentucky, area. The faunas introduced by this Gulf 

 invasion continued through the later Onondaga and Hamilton epochs, 

 persisting in the Louisville area, extending far to the north into 

 Canada, and migrating around the Cincinnati axis into the western 

 part of New York. 



This is the interpretation of the faunal conditions of that time given 

 by Prof. Charles Schuchert, in his Paleogeography of North Amer- 

 ica,- based upon general paleontological evidence ; and the occurrence 

 of the crinoid forms under consideration is in perfect agreement with 

 it. The principal colony was in the Louisville area, where these 

 forms appear in rocks of Onondaga age, culminating and becoming 

 extinct in the succeeding Hamilton. They spread northw^ard and 

 northeasterly, into Michigan, western New York, and adjacent Cana- 

 dian localities. No representative of these genera is known outside 

 of the limits thus indicated. 



The leading type in abundance, so far as our collections show, was 

 Dolatocrinus , which from a few well-marked species in the Onondaga 

 increased to great profusion in number and variety, reaching its 

 acme in the Hamilton, where it is represented by numerous species. 

 But whereas in the Onondaga the species were extremely well defined, 

 rapid development ensued in the Hamilton under conditions favor- 

 able to a rampant growth, in which certain characters, stable and 

 thoroughly reliable in the earlier formation, become worthless for 



1 Springer. On the crinoid genus Scyphocrinus, 1917, p. 25. 



2 Bull. Geol. Soc. Amer., vol. 20 (1910), pp. .540, 544-545. 



