216 aASTEROPODS. 



rowly lanceolate, and about one-third as long as the entire length 

 of the shell. Surface glabrate. 



Horizon and localities. Lower Silurian, Trenton limestone : 

 McCune (Pike county). 



As remarked by Meek, it is almost impossible to distinguish, 

 generically, between Subulites, Conrad, and Polyphomopsis, 

 Portlock. But as Conrad's genus was proposed first, it makes 

 little difference, insofar as the name is concerned, whether or not 

 the two are synonymous. They are probably not. It must be 

 admitted, however, that Conrad's term was unaccompanied by a 

 description, but his figures give a much better idea of the kind 

 of a shell he had under consideration than a large proportion 

 of the early genera proposed without figures. It is extremely 

 curious, and indeed unfortunate, that among the dozen or more 

 species described from North America, there is not a single 

 one that shows clearly the structural characters of the shell. 

 The group, however, is evidently a good one. and can be used 

 advantageously, notwithstanding its imperfections. 



Doubtful Species. 



Murchisonia ozarkensis Shumard. 1863: Trans. St. Louis Acad. Sci., vol. 

 II, p. 106. Magnesian limestone: Oza'k county. Cast. 



BellerophonscissileConTSid, 1846: Proc. Acad. Nat. Sci., Phila., vol. II, p. 

 175. Kaskaskia limestone : Ste. Genevieve county. 



Macrochilus blairi Miller, 1891: Geol. Sur. Indiana, 17th Ann. Rep., Adv. 

 sheets, p. 86, pi. xiv, figs. 5-6. Chouteau limestone: Sedalia. 



Trochita carbonaria Meek & Worthen, 1866: Proc. Acad. Nat. Sci., Phila- 

 delphia, p. 270. Kaskaskia limestone : Ste. Genevieve county. 



