TRENTON LIMESTONE. 217 
ever, has already been said in reference to this part of the subject, and new facts are 
constantly presenting themselves in favor of the views here advanced, which, from their 
novelty, and the imperfection and obscurity of many of the specimens, have heretofore 
been regarded as untenable and unsatisfactory.* 
Position and locality. This specimen is from the valley of West-Canada creek, near 
Middleville, and in the same position as those previously noticed. (Cabinet of Dr. Emmons.) 
Pruate LIX. 
In the figures 1, 2, 3, I have attempted to give the precise markings presented on the 
surface of the varieties of E. proteiforme, which are somewhat more distinct than the litho- 
graphic impressions. 
Fig. 1 a, b. var. tenuiteztum. The surface markings on two different specimens, somewhat enlarged 
beyond the natural size. 
Fig. 2 a, b. var. tenwistriatum. The surface markings on two different specimens, both slightly mag- 
nified. A careful examination shows a slight difference in the strength of the markings, 
which becomes more extreme in other specimens. 
Fig. 3 a. var. lineolatum. This one presents only transverse strie ; but some specimens show minute 
longitudinal ones, passing into the preceding variety. 
Fig 3. var. lineolatum. The surface is covered by fine spots or stigmata, as if some adhering softer 
substance had been separated from it. The same is observed in fig. 2 b, in a less degree. 
The markings are very similar to the bases of the cells of a Fiustra. 
279. 11. ENDOCERAS ARCTIVENTRUM (x. sp.). 
Pu. LI. Figs. 2 a, 6. 
Elongated, very gradually tapering ; septa distant about one third the diameter of the 
shell ; siphuncle marginal (ventral), slightly contracted at the junction of the septa; 
section oval ( probably from compression ); embryo tube slender. 
The specimen is a fragment, preserving about eight or nine of the chambers; but these, 
with the siphuncle, are different from any other species of this period. The siphuncle is 
remarkably narrow, somewhat longitudinally wrinkled, and slightly contracted at the 
junction of the septa. 
The small embryo tube contains a young shell, which has the appearance, in a small 
portion visible, of Orthoceras junceum ; but this cannot be demonstrated till we obtain 
other specimens. 
Position and locality. This species occurs, associated with the preceding, in the higher 
part of the Trenton limestone. 
* This view of the development of the OrrTHocrRATA was first imperfectly made known at the meeting of the 
American Association of Geologists and Naturalists, at Washington, in 1844, and subsequently more fully explained 
at the New-York meeting in 1846. 
| PaLzonTo.oey.] 28 
