TRENTON PERIOD. 



213 



(b.) Brachiopods.— Figs. 286, 287, Orthis Lynx ; 2S3, 0. occidentalis ; 289, 0. 

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

 Strophomena rugosa (formerly Leptsena depressa) ; 293, Stroph. alternata ; 294— 

 296, Rhynchonella increbescens H. : 297, 298, Rhynclionellaf bisulcata. 



(c.) Concliifers. — Fig. Z§\, Acicula ? Trentonensis Con.; 302, Ambonychia belli- 

 stnata H. ; 303, Ctenodonta nasuta ; also Gonocardium immaturum B., of Black 

 River limestone on the Ottawa, Canada, and species of Modiolopsis. 



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

 donta nasuta. 



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

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

 inches long; 307, Helicotoma p>l<* nv lata Salter, from Canada; 308, Bellerophon 



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

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

 compressus ; 311, C. Trentonensis. 



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

 311, 312, Cyrtolites Trentonensis, side-view. The genus Cyrtolites is like a partly- 

 uncoiled 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. vertebrale H., also Trenton, the figure reduced to one-third; 315, part 

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

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



