216 
PALJEONTOLOGY OP NEW-YORK. 
278. 10. ENDOCERAS PROTEIFORME 1 var. ELONGATUM. 
Pl. LII. Fig. 1 a, b. 
Teretely cylindrical, very gradually tapering and extremely elongated ; septa distant 
about one sixth to one fifth the diameter of the shell ; siphuncle large, excentric. 
This species is closely allied to E. protefcforme , in the character of septa and siphuncle. 
The external shell and embryo tubes have not been discovered, and it is from the great 
size of the siphuncle that I have referred the species to the Genus Endoceras. It is usually 
found in fragments, which are more or less compressed and distorted. The one figured is a 
small portion of a much larger specimen which was imbedded in a nearly perfect condition, 
but is broken from the weathering and decay of the rock. 
Fragments of this species are not unfrequent in the higher part of the Trenton limestone, 
but, like all the others attaining great size, it is nearly impossible to procure characteristic 
specimens. 
Fig. 1 a, b. Parts of the same individual, united as represented by the dotted line. 
Position and locality. In the higher shaly beds of the Trenton limestone at Middleville. 
ENDOCERAS PROTEIFORME. 
Pl. LVIII. Fig. 1. 
Reference page 208-of this Report. 
Since the preceding pages were in press, I have obtained from Dr. Emmons the specimen 
figured on Plate LVIII. It is apparently identical with the preceding, and very similar to 
the var. elongatum , if this be a distinct variety of so variable a species. This one shows 
very conclusively that the young shell is developed within the siphuncle of the parent one, 
and furnishes more evidence than any other instance I have seen, that the old shell is 
succeeded by the young one, which assumes the place of the parent, which gradually 
decays. The specimen preserves twelve or more chambers of the parent shell, which are 
pierced by an extremely large submarginal siphuncle. This siphuncle embraces the young 
shell, which projects beyond the last septum of the old one preserved, nearly ten inches, 
and is imperfect at its extremity. The part of the young shell thus projecting, numbers 
between forty and fifty chambers, the lower or larger part of it being partially enclosed 
by the embryo tube. 
Two specimens of this character have been found, and, when taken in connexion with 
the preceding illustrations, leave little doubt as to the actual mode of development among 
the shells of this genus. It would appear from this one that the embryo tubes and young 
shells within keep pace in their growth with the parent, all the specimens of the young 
bearing a uniform proportion to the size of the enclosing or parent shell. Sufficient, how- 
