Characterized by its enormous size, attaining lengths of up to 15 feet
Submarginal siphon large
Septa spaced further apart moving towards the body chamber
Shell/Spihuncle diameter ration roughly 2:1
Endoceras proteiforme from McMillan formation of Kenton County, Kentucky(OUIP 724, left) and Kope formation of Grant County, Kentucky (OUIP 233, right)
Cephalopod. Top view of a fragment of internal mold of a straight, conical shell, broken lengthwise. Note siphuncle protruding where rest of the specimen is missing; in Endoceras the siphuncle is large and well of the center of the conical shell. Figure about 1/3 natural size. Exact range unknown, thought to be entire Cincinnatian.
McFarlan (1931) :
E. proteiforme is characterized by its enormous size, sometimes attaining a length of 10-15 feet, circular section, comparatively shallow chambers, and large submarginal siphon. The spacing of the septa increases toward the body chamber. Relative diameters of the shell and siphuncle in available specimens about 2:1. A wide-spread and common species throughout the Mohawkian and Cincinnatian.
Hall (1847) :
General from cylindrico-conical, more or less elongated, often compressed, tapering somewhat unequally in different specimens; young specimens terminating in an extremely acute point; surface marked by distinct transverse striae, which usually appear like narrow subimbricating bands, with one edge well defined and more elevated than the other, more or less distinctly striated longitudinally, striae varying from extreme tenuity to distinct elevated threadlike lines; section circular; septa distant from one fifth to one fourth the diameter; siphuncle eccentric or submarginal.
I am able to characterize three distinct varieties of this species, which are the prevailing forms: these depend mainly on the surface marking of the young shell. The old shells are recognized by a large submarginal siphuncle, which usually contains a smooth cylindricoconical embryo tube or sheath. This tube is sometimes irregularly tapering, and always free from visible surface markings or sculpture. Within this embryo tube are the young shells, sometimes perfectly formed Orthocerata and at other times destitute of septa or siphuncle. These young shells are also frequently found separate from the parent shell or embryo tube, when we are compelled to rely upon the surface markings for their determination. The position of the siphuncle, convexity of septa, and some other characters, are usually constant in all the varieties, which only exhibit a change in the character of the surface. In the absence of septa and siphuncle, which is of common occurrence in the young shell, the character of the surface is reliable for determining the species.
