the Morphology of tlie Blastoidea. 249 



Pentreinites Inpijramidalis^ Hall. Keokuk limestone 

 (Subcarboniferous) , Missouri. 



P. clavatus^ Hambach*. Subcarboniferous, Illinois. 



P. Grosvenori^ Slmmard. Archimedes limestone (Subcar- 

 boniferous) , Indiana. 



P. lineatus^ Shumard. Encrinital limestone (Subcarbo- 

 niferous) , Illinois. 



P. Reinwardtii^ Troost. L. Helderberg group (Upper 

 Silurian), Kentucky. 



P. suhcylindrica^ Hall. Niagara group (Upper Silurian), 

 Ohio. 



P. suhfnaicatus, Hall, Hamilton group (Up. Devonian), 

 Iowa, 



P. Woi-fheni, Hall. Keokuk limestone (Subcarboni- 

 ferous), Iowa &c. 



If all the above species are rightly placed under Troosto- 

 crt'nus, the genus then made its first appearance in the Upper 

 Silurian, reappeared in the Upper Devonian, and culminated 

 in the Carboniferous. We are not acquainted with any 

 Troostocrinus from the Palreozoic rocks of this country or of 

 the continent ; so that it appears to be entirely an American 

 genus. 



Genus Orophocrinus, Von Seebach, 1864. 



Oro2)hocrimis, vou Seebacli, Nachr. k. Gesellsch. zu Gottingen, 1804, 



p. 110. 

 Codonites, Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, 



1809, p. 84 (note) ; Meek aud Wortheu, Illiuois Geol. Survey Report, 



1873, V. p. 403. 



Ohs. Von Seebach was the first to point out the distinction 

 of this generic type from that of the ordinary Peutremites ; 

 and although it received the name Codonites five years later, 

 we feel bound to follow Ludwig and Zittel in using Von 

 Seebach's name rather than that of the American authors. 

 Both chose for their type the Pentremites stelUforiiiis^ Owen 

 and Shumard. 



The second description by Meek and Worthen is sufficiently 

 explicit to make it unnecessary for us to redescribe the genus ; 

 we need only at present point out a few of its peculiarities, 

 more especially in connexion with the European species. 



But two species of Oropliocrinus are at present known, 

 both of them from the American Carboniferous series, viz. 



T. Reimvardti and T. lineatus ; but the other species agree so well in form 

 and outline with these, that we can hardly duubt their generic identity. 

 * Non P. davatus, Schultze, Devonian, Eifel, 



