TRENTON PERIOD. 



215 



Fig. 319 represents Conularia gracilis H., a delicate four-sided pyramid, 

 apparently admitting of some motion at the angles, but having septa within 

 in the smaller extremity (a), and supposed therefore to he 

 the shell of a Cephalopod ; b is an enlarged view of the -Fig. 319. 



surface. 



4. Articulates — (a.) Trilobites. — Fig. 320, Asqphus 

 (Isotelus) gigas, a small specimen; the species is sometimes 

 ten inches or a foot long; fig. 321, Calymene senaria Con. ; 

 fig. 321 a, same rolled up, by bringing the tail to the head; 

 fig. 322, Lichas Trentonensis ; fig. 323, Trinucleus concen- 

 tricus ; figs. 324, 325, Agnostus lobatus, H., head and tail 

 portions magnified; 326, natural size. 



(b.) Ostracoids. — Fig. 327, Leperditia Fabulites? Con., 

 natural size; a, b, transverse and vertical sections, the 

 specimen from Canada (L. Josephiana Jones, who refers 

 the species with a query to the Fabulites of Conrad). 



In the State of New York the Black River limestone is especially remarkable 

 for its great abundance of species of the Orthoceras family, among which are 



Conularia gracilis. 



Figs. 320-327. 



Crustaceans.— Fig. 320, Asaphus gigas (X %); 321, a, Calymene senaria; 322, Lichas Tren- 

 tonensis; 323, Trinucleus concentricus; 324, 325, Agnostus lobatus (X4); 326, same, 

 natm-al size ; 327, a, b, Leperditia Fabulites (natural size). 



the species Onnoceras tenuifilum H., Endoceras longissimum PL, and Gonio- 

 ceras anceps, which do not recur in the overlying Trenton limestone. Some of 

 them are, however, found in rocks in Canada whose fossils are two-thirds those 

 of the Trenton ; and both there and in Tennessee, as well as other parts of the 

 West, there is a mingling of Black River, Birdseye, and Trenton fossils, which 

 proves that the rocks make but one group. (Billings.) 



The number of Chazy species occurring in the Trenton group has not been 

 recently announced. 



