The genus Endoceras was proposed by Hall (Pal. N. York, vol. i., p. 58) for a group of Orihocerata; having “a large siphunele, mostly lateral or excentric, marked or ridged on the outer surface by the septa, which, from their oblique direction, give it the appearance of a tube with spiral lines. Within this siphunele are one or more very elongated eonical tubes, often one within the other to the number of four or five.” The leading point, then, in the definition of Endoceras is the possession of a multiple siphunele, composed of two or more concentric tubes placed one within the other, each tube having the form of an elongated cone.