﻿498 



Coelogasteroceras. 



This genus was described in my " Carboniferous Cephalopods/' 

 second paper, Fourth Ann. Rep. Geol. Texas. 



Coelogasteroceras canaliculatum of the Carboniferous has an 

 umbilical perforation of considerable size, but the history of the 

 impressed zone is similar to that of Anomaloceras. One section 

 was obtained shown in Fig. 33, PL x. This cut across the meta- 

 nepionic as it was changing in form on its passage into the para- 

 nepionic substage and shows the dorsum becoming flattened and an 

 outline transitional to the full nephritic outline of the paranepionic, 

 which is drawn below at a plane which passed through this substage 

 just before the apex was reached. In making this section, the apex 

 was seen and passed through by grinding. 



The size and shape of the umbilical perforation in this species 

 does not justify the assumption that the dorsal furrow could have 

 resulted from the abrupt bending of the volution at the gyroceran 

 bend. The curvature of the first whorl is gradual ; the expansion of 

 the volution laterally and ventro-dorsally is not remarkable. The 

 diameter of the umbilical perforation was four millimetres in one 

 specimen and in the section figured it was somewhat less at the same 

 points. The increase by growth was also approximately the same 

 in both of these fossils. 



Unfortunately the absence of a dorsal furrow on the dorsum of 

 the metanepionic substage was not demonstrable with unquestion- 

 able certainty in either of these specimens, but it seemed to be 

 entire and gibbous in both as given in the figure. 



The shell is apparently smooth in the nepionic stage, although 

 this may have been in part due to the condition of preservation. 

 It is obvious that there are no lateral furrows or ridges as in Colo- 

 ceras at any stage. Faint transverse folds were observed in the 

 neanic stage of one specimen, and the abdomen and lateral zones 

 become flattened at the same time. A hollow, central, ventral zone 

 appears in the anephebic substage and persists throughout the 

 ephebic stage. 



The sutures are nearly straight in the nepionic, and then acquire 

 a slight ventral lobe in the neanic stage ; this deepens in correlation 

 with the ventral hollow zone in the ephebic stage, and the lateral 

 lobes and saddles on the umbilical shoulders also become more 

 marked in this stage. 



