58 PALEONTOLOGY OF NEW-YoRK. 
90. 2. ORMOCERAS TENUIFILUM? var. DISTANS. 
Pu. 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 Ormoceras Bayfieldii (StoxEs, 
Geol. Transactions, 2d series, Vol. i. pl. 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. ORMOCERAS? GRACILE (n. sp.). 
Pu. XVII. Fig. 3. 
Slender, elongated, very gradually tapering ; septa distant about 4 of the diameter ; 
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 OrmMoceERAS. 
Position and locality. Watertown, in the Black-river limestone. 
(Cabinet of the Albany Institute.) 
Genus ENDOCERAS. 
[ Greek, evdov, within, and xepas, 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 ctinoceras of Bronn ; but 
the foundation of this name implies an impossibility, and requires a structure incompatible 
with the economy of the OrtHoceERArTa ; and, therefore, for our specimens at least, we must 
substitute another.* 
* J shall be able to show, under the OrTHocERATA of the Trenton limestone, that such a structure as that of rays 
in verticillations from the internal tube to the walls of the siphon could never exist in an animal constituted like the 
Orthoceras. 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 tube 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. 
