CARBONIFEROUS CEPHALOPODS. 335 



it resembles T. cavatum closely in general aspect. It differs from this, how- 

 ever, in the proportionally narrower abdomen, and the umbilical shoulders 

 are also narrower and more abrupt. The great differences are of course in 

 the absence of abdominal tuoercles and in the sutures, the peculiar broad ab- 

 dominal saddles of T. cavatum being absent. There is a shallow abdominal 

 lobe on the impressed zone of the dorsum. The involution does not extend 

 beyond the lateral lines of nodes. The living chamber is probably not much 

 over one-fourth of a volution in length, judging from the length of that in 

 the original specimen in my collection, which has the chamber complete on 

 the venter. The siphuncle is situated above the centre. There is also a 

 specimen in Prof. Newberry's collection at Columbia College, New York, 

 from Kansas City, Missouri, with an entire living chamber which is even 

 slightly shorter than one-fourth of a volution in length. 



The young as shown above in the figure of a specimen (Figs. 30, 31) from 

 Dr. Newberry's collection, reported to have come from Miami County, Illinois, 

 is of an entirely different appearance from the later stages, with an almost 

 round whorl, sutures nearly straight or with only a slight abdominal saddle, 

 shell smooth and umbilical perforation large, showing that they were true 

 cyrtoceratites throughout the first whorl, which was not completed until the 

 shell had reached a considerable size. The amount of involution of the younger 

 whorls by the living chamber is exaggerated in the side view of this specimen 

 (Fig. 31), and is better indicated in the front view of the same. The resem- 

 blance of the young whorl in outline to that of the genus Temnocheilus can 

 be readily seen in the last figure in which the front view of the first part of 

 the second whorl is shown. On this second whorl a single row of tubercles 

 appears on either side, and theee complete the resemblance to Temnocheilus. 



