Middle Ordovician – Late Ordovician
Endoceras is an extinct genus of nektobenthic carnivores
Identification in Hand Sample:
- Conchs large, straight, with annuulations varying from low and closely spaced to well elevated and distinctly apart
- Sutures straight, transverse
- Siphuncle large, ventral holochoanitic
- Endocones subcircular in cross section
- Endosiphunclular tube thin
Treatise on Invertebrate Paleontology, Part K, Mollusca 3 (1964):
- Conchs large, straight, similar to Cameroceras, but with annuulations varying from low and closely spaced to well elevated and distinctly apart; cross section slightly depressed; sutures straight, transverse. Siphuncle large, ventral holochoanitic; endocones subcircular in cross section; thin endosiphunclular tube; apical part unknown.
- Othocones with large, more or less eccentric siphuncle, the funnels extending only to the next preceding septum
- I propose this term, at least provisionally, to include those species of the Orthocerata which have a large siphuncle, mostly lateral or eccentric, 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 the siphuncle are one or more very elongated conical tubes, often one within another to the number of four or five.
- The latter character is one of the essential features of Actinoceras of Brown; but the foundation of this name implies an impossibility, and requires a structure incompatible with the economy of the Orthocerata; and, therefore, for our specimens at least, we must substitute another.