496 PALAEONTOLOGY OF ILLINOIS. 



Po&ition and locality: The specimens are attached to the sur- 

 face of a slab of rock labelled only "Keokuk limestone.'' This 

 is probably an error as the character of the rock is decidedly 

 like that of the St. Louis limestone at Alton, 111. 



COSCINIUM Keyserling, 1846. 



(Eeise in das Petschora Land, p. 191.) 

 (For generic diagnosis see page 385.) 



So far as I am aware the minute characters of the type of 

 this genus have never been made public, so that there is yet a 

 possibility of error when we refer species here. The probabili- 

 ties, however, are decidedly against C. cyclops Keys., being 

 generically distinct from such species as C. cribriforme Prout, 

 and C. latum, of the present work. These two species belong to 

 a small group that is first met with in the Upper Helderberg, 

 and extends up into the Coal Measures. The form of the 

 zoarium is precisely like that of Chithropora Hall, and authors 

 have usually regarded that genus as synonymous with Cosci- 

 nium. This is an error if my understanding of C. cyclops is 

 correct, since Hall's genus is closely related to Ptilodictya Lons- 

 dale, while Coscinium, as defined by me, is an unquestionable 

 member of the CYSTODICTYONID^E. In 1859, Prout identified a 

 species from the Falls of the Ohio with the C. cyclops, and at 

 the same time described a new species from the same locality as 

 C. cribriforme. In my "American Palaeozoic Bryozoa," I also 

 described and figured a species as C. cyclops. During the pro- 

 gress of this work I have made it a duty to reconsider every 

 previously determined point. In this case the result was more 

 than usually gratifying, since I can now rectify several errors. 

 I learn that the C. cyclops of Prout, is the Clathropora inter- 

 texta Nich., (a true species of that genus) and not the same as 

 Keyserling's species; that my C. cyclops and Hall's Clathropora 

 carinata (later Coscinotrypa carinata) are the same as Coscinium 

 cribriforme Prout. With regard to the true C. cyclops, I shall 

 hold that it is not known in the rocks of this country. In rela- 

 tion to the generic characters of this species I have only this 

 to say, that every zooecial feature mentioned by Keyserling 



