Baltoceratidae

The Baltoceratidae comprises a family of nautiloid cephalopods from the lower and middle Ordovician included in the Ellesmerocerida. Shells are smooth, long and straight. Septal necks in the siphuncle are straight (orthochoanitic) and connecting rings are thin and homogeneous.

Origin is within the Ellesmeroceratidae, the family in turn giving rise to the ellesmerocerid Cyclostomideratidae and to the Orthocerida. The siphuncle tube lacks the diaphragms characteristic of more primitive ellesmerocerids and the primitive ventro-marginal siphuncle becomes more central.

The Baltoceratidae is divided between those with empty siphuncles including Rioceras, Endorioceras, Eobactrites, and Baltoceras, and those in which the siphuncle is rod-bearing, examples Cyptendoceras and Rhabdiferoceras.

References:

Rousseau H. Flower 1964, The Nautiloid Order Ellesmerocerida (Cephalopoda). New Mexico Bureau of Mines and Mineral Resources Memoir 12.

W.M. Furnish and Brian F. Glenister 1964, Natiloidea - Ellesmerocerida. Treatise on Invertebrate Paleontology, Part K.