58 PAUBONTOLOGT OF NEW-TORK. 



90. 2. ORMOCERAS TENUIFILUM1 »ar. DISTANS. 



Pi,. XVII. Fig. 2. 



Form as previously described ; septa a little more distant ; form of siphuncle, as appears 

 near the base, somewhat different, and resembling very nearly Ortnoceras Bayfieldii (Stokes, 

 Gtol. Transactions, 2d series, Vol. i. pi. 9, fig. 1 ). A partial longitudinal section on the 

 opposite side displays the same structure as figs. 1 c, d, e, on the previous plate, and I have 

 regarded this as a variety of the last species. 



The specimen before us is worn down to the siphuncle only towards the lower part of 

 the figure ; and the peculiar form there presented is probably owing to weathering, or some 

 accident, as I have seen the same in another specimen since this was figured. 



Position and locality. With the preceding. 



91. 3. ORMOCERASI GRACILE (n. *p.). 



Pl. XVII. Fig. 3. 

 Slender, elongated, very gradually tapering ; septa distant about J of the diameter j 

 siphuncle? surface? 



This species is distinguished by its more slender form and distant septa. The siphuncle 

 is not distinctly visible ; but from some other evidences, it is presumed to belong to the 

 Genus Ormoceras. 

 Position and locality. Watertown, in the Black-river limestone. 



(Cabinet of the Albany Institute.) 



Ge»u8 ENDOCERAS. 

 [Greek, Evfov, within, and xifog, a horn.] 



I propose this term, at least provisionally, to include those species of the Orthocerata 

 which have a large siphuncle, mostly lateral or excentric, marked or ridged on the outer 

 surface by the septa, which, from their oblique direction, give it the appearance of a tube 

 with spiral lines. Within this siphuncle are one or more very elongated conical tubes, often 

 one within another to the number of four or five. 



This latter character is one of the essential features of the Jictinoceras of Bronn ; but 

 the foundation of this name implies an impossibility, and requires a structure incompatible 

 with the economy of the Orthocerata ; and, therefore, for our specimens at least, we must 

 substitute another. • 



* I shall be able to ihow, under the Okthocerata of the Trenton limestone, that such a structure as tliat of rays 

 in verticillations from the internal tube to the walls of the siphon could never exist in an animal constituted like the 

 Orthoeerat. These tubes, being developed one within the other, and remaining within the siphuncle only temporarily, 

 and capable of separation without injury to either the young lube or the parent shell, could never have been provided 

 with verticillating rays to sustain themselves in that position. We have also such numbers of them separated from the 

 parent shell, that had there been any such structure, some indications of it would have been preserved. 



