TRENTON LIMESTONE. 219 
283. 15. ENDOCERAS APPROXIMATUM (pn. sp.). 
Pu. LIV. Fig. 2 a, 
Cylindrical, gradually tapering ; septa with a convexity little more than one fourth their 
diameter, distant about one fifth the diameter of the shell; siphuncle large, marginal, 
obliquely annulated by the thin edges of the septa. 
This specimen is a fragment, preserving about five or six chambers, with a portion of the 
siphuncle projecting above. 
In many respects, this species resembles the E. proteiforme ; but the markings of the 
septa upon the siphuncle are more approximate in proportion to its diameter. In the one 
figured, they are distant about one third the diameter of the siphuncle; being actually 
nearer than those of smaller siphuncles of that species figured on Plate L, which are distant 
two fifths of the diameter of the tube. 
There is, however, still some obscurity in regard to these parts of the shell, and we are 
not able to decide whether their proportions are constant. This can only be determined by 
a comparison of all the parts of a large number of specimens of authentic species. I have 
examined three specimens of what appear to be, very satisfactorily, the siphuncles of E. 
proteiforme, two of them containing a portion of the embryo tube. In all these the diameter 
is almost precisely the same, and the distance of the septa corresponds. On this account, I 
have thought it preferable to indicate this one as a distinct but approximating species. 
Position and locality. This species is found, associated with the preceding, in the higher 
part of the Trenton limestone near Middleville. 
284. 16. ENDOCERAS DUPLICATUM (n. sp.). 
Pu. LV. Fig. 1. 
Cylindrical, gradually tapering ; septa distant about three eighths of an inch; siphuncle 
extremely distended, and containing two embryo tubes, within each of which is a young 
shell. 
The only specimen seen is much compressed, and distorted so that its original form can 
not be made out. It evidently contains two embryo tubes, which apparently belong to the 
specimen. This is quite distinct from the Endoceras gemelliparum of the Black-river lime- 
stone, both in its general form, distance of septa and character of the tubes, showing a 
second species with double embryo sheaths. 
Position and locality. This species occurs in the upper shaly part of the Trenton limestone 
near Middleville. (Cabinet of Joun GeBuarp, Jr.) 
28* 
