TRENTON PERIOD. 



213 



(6.) Brachiopods.—E\gs. 286, 287, Orthis Lynx; 288, 0. occidentalis ; 289, 0. 

 testudinaria Dal. ; 290, 0. tricenaria Con. ; 291, Leptsena sericea Sow. ; 292, 

 Strop>homena mtgosa (formerly Leptsena depressa) ; 293, Stroph. alternata ; 294- 

 296, Rhynchonella increbescens H. ; 297, 298, Rhynchonella ? bisulcata. 



(c.) Conchifers. — Fig. 301, Avicula ? Trentonensis Con.; 302, Ambonychia belli- 

 striata H. ; 303, Ctenodonta nasxita ; also Conocardium immaturum B., of Black 

 River limestone on th'e Ottawa, Canada, and species of Modiolopsis. 



Figs. 301-303. 



Conchifers. — Fig. 301, Avicula? Trentonensis; 302, Ambonychia bellistriata; 303, Cteno- 

 donta nasuta. 



(d.) Gasteropods. — Fig. 304, Pleurotomaria lenticidaris Con., very common in 

 the Trenton limestone; 305, Murchisonia bicincta ; 306, M. bellicincta, often four 

 inches long; 307, Helieotoma planulata Salter, from Canada; 308, Bellerophon 



Gasteropods. — Fig. 304, Pleurotomaria lenticularis; 305, Murchisonia bicincta; 306, M. 

 bellicincta; 307, Helieotoma planulata; 308,309, Bellerophon bilobatus; 310, Cyrtolites 

 compressus ; 311, C. (?) Trentonensis , 312, id., dorsal view. 



bilobatus, very common; 309, same, side-view; 310, Cyrtolites compressxis H; 

 311, 312, Cyrtolites (?) Trentonensis. The genus Cyrtolites is like a partly-un- 

 coiled Bellerophon, and is not chambered. There are also several Patella-like 

 species of Metoptoma (formerly Capulus and Patella), a genus which began in the 

 Calciferous beds. 



(e.) Cephalopods. — Fig. 313, Orthoceras junceum H, a small Trenton species ; 

 314, O. vertebrate H., also Trenton, the figure reduced to one-third; 315, part 

 of an Ormoceras tenuifilum, showing the beaded siphuncle and septa. The spe- 

 cies is very common in the Black River limestone, and is sometimes over two 



