298 



ORTHOCERAS. 



0. vertebrate (Hall.) This shell is cylindrical, very gradually tapering, annulated with abruptly elevated 

 angular ridges, which are distant from each other about one-fourth the diameter of the tube, slightly aichcd 

 upon the back, and direct on the ventral side ; surface marked by strong longitudinal strite and finer trans- 

 verse ones, giving it a cancellated appearance ; siphuncle apparently central or subcentral. 



FIG. 208. 



Orthoceras vertebrale. 



We have found this species only 



Fio. 209. 



FIG. 210. 



Fig. 208 represents the ventral side of a fragment of the 0. vertebrale. 

 in the Black River limestone of Isle La Motte. 



0. anellum (Con.) This shell is elongated, very gradually tapering, annulated by prominent sharp 

 slightly sinuous ridges which are distant about one-fourth the diameter of the shell, longitudi- 

 nally marked by fine crowded wrinkled stria) ; septa moderately 

 convex ; siphuncle eccentric, but not marginal ; section circular. 



This species is readily distinguished from all others by its angu- 

 lar approximative angulations, which are sharper and more elevated 

 than those of any other species. 



Fig. 209 represents a fragment of the septate portion of the shell 

 of the 0. anellum. It is found with the preceding species in Isle 

 La Motte. 



0. amplicameratum (Hall.) Tcretely cylindrical, extremely elon- 

 gated, very gradually tapering ; outer chamber profound ; septa 

 distant about one-third of the diameter, very convex ; siphuncle 

 excentric, small ; surface (?) section circular. This species is distinguished 

 from all others in the Trenton limestone by its great length and very gradual 

 diminution from the larger extremity, and the distant and very convex septa. 



Fig. 210 represents a fragment of the septate portion of a large shell of 

 the 0. amplicameratum. The specimen was found in South Hero, in Tren- 

 ton limestone. 



0. strigatum (Hall.) Elongated, teretely cylindrical, gradually tapering ; outer chamber large ; septa 

 distant about one-fifth the diameter of the shell, very convex ; siphuncle small, central ; surface marked by 

 flexuous elevated longitudinal lines, which are indistinctly visible on the cast. 



FIG. 211. 



Orthoceras amplicameratum. 



Orthoceras strigatum. 



Fig. 211 represents a fragment of a large specimen of this species. About twenty of the chambers are 

 preserved, as well as a large part of the outer chamber. There is also present a small septate tube within 

 the open extremity. This occurs in the upper part of the Trenton limestone, in Grand Isle. 



0. multicameratum (Con.) Extremely elongated, slender, very gradually tapering to an acute point; 



