New Mexico Geological Society Annual Spring Meeting — Abstracts

The nautiloid cephalopod Domatoceras Hyatt 1891 is well known from the Pennsylvanian and Permian of North America. Descriptions however are pretty much limited to the external morphology of the shell as in Bernhard Kummel (1964: Nautiloidea - Nautilida. Treatise on Invertebrate Paleontology Part K) and others. Mention of the siphuncle is limited to its position and the possibility of its being orthochoanitic.

The segments of the siphuncle and part of a fourth are exposed in a break in specimen P 56221 of the New Mexico Museum of Natural History and Science, that have allowed description for perhaps the first time. Segments are 5 mm in length, fusiform, expanding from 2 mm at the septal foremina to as much as 3.5mm at the midpoint. Septal neck are not recognized, however the slight expansion suggest that, when present, they were slightly cyrtochoanitic, rather than orthochoanitic as inferred in the literature.