TRENTON LIMESTONE. 215 
more suddenly contracted and aculeate near the apex. This character does not probably 
influence the young shells developed within them. 
Figs. 2c, d. Parts of the siphuncle separated from larger shells, still retaining the embryo tube within. 
Several such specimens have been found, though none in which the embryo tubes contain 
young shells. The similar character in these tubes, with the marks of septa upon the si- 
phuncle equally distant with the preceding figures, appears to be sufficient to warrant their 
reference to the same species. The siphuncle is marked by oblique or ascending annulations, 
indicating the junction of the septa. This ascending direction of the annulations is due to the 
lateral or excentric position of the siphuncle. The slight variation in the distance of the septa, 
as marked on the siphuncle, is no more than is shown in different specimens in the preceding 
figures. 
Fig. 3. An embryo tube, more conical than any of the others. I have referred it, with some hesitation, to 
the same species, until further discoveries shall prove it distinct. 
Pruate LIII. 
Fig. 2. A large fragment of this species, in which the embryo tube is preserved, while the surrounding 
shell has been partially removed. All that part of the parent shell remaining is septate, the 
outer chamber having been broken off; which is likewise true of all other specimens of this 
species that have fallen under my notice. 
Position and locality. This species is found in the central and higher part of the Trenton 
limestone at Middleville and the valley of West-Canada creek, where it is far more abun- 
dant than any other species in the rock. It oecurs less frequently at Turin, Lowville and 
Watertown, as well as in the same position in the Champlain valley. (State Collection.) 
I have been inclined to regard this species as very closely allied to, if not identical with, 
Orthoceratites duplex, as described by WantEeNBERG and Hisincer (ct. Soc. Sci. Upsal, 
Vol. viii, p. 88; Leth. Suecica, pag. 28, pl. 9, fig. 1); but the figures given by pr Vrr- 
nevIL (Pal. Russia and the Ural Mountains) differ from that of Histyeer in the distance of 
the septa, and in having the siphuncle quite marginal. This difference will be seen by a 
comparison of the figures here given, with those of the author last cited (pl. 24, fig. 7, 
and pl. 25, fig. 2 a, 6), where the distance of the septa is comparatively greater, and the 
siphuncle larger and quite marginal. The young shells of this species, however, are re- 
presented as constricted near the aperture, as in the one under consideration. It is not 
improbable that more than a single species is known in Europe under the name of O. 
duplex, and the Endoceras proteiforme is represented in one of them. 
For synonyms and references of O. duplex, see page 220, under Endoceras distans. 
