INVERTEBRATES. 389 



smaller end, 1.25 inches; greater diameter at the aperture, 

 about 1.24 inches ; smaller ditto, 0.92 inch ; greater diameter at 

 the smaller end, 0.54 inch; smaller ditto, 0.43 inch. 



This species has somewhat the form and general appearance of C. depressum, 

 Goldfuss, but is less compressed, and differs in being a little flattened on the 

 sides ; while its siphuncle is smaller, and not so near the dorsal margin. As 

 near as can be determined by the direction of the lines of growth on our shell, 

 it would also seem to differ in having the lip more prominent on the dorsal side. 

 It is a very remarkable, rapidly expanding form, that may possibly belong to 

 an undescribed genus. 



Locality and position : Grayville, Illinois; Upper Coal Measures. 



Ctrtoceras? dilatatum, M. and W. 



PI. 29, fig. 2. 



Cyrtoceras ? dilatatum, Meek and Worthen, October, 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 468. 



Shell broadly conical, very rapidly expanding, rather thick 

 especially on the ventral side, slightly curved and apparently 

 somewhat compressed on the dorsal and ventral sides. Surface 

 ornamented by numerous, distinct, regularly arranged, subim- 

 bricating, annular marks of growth. Septa at about two inches 

 from the smaller end, separated by spaces equaling near one- 

 twelfth of the greater diameter of the shell at the same place. 

 Siphuncle and form of the aperture unknown. Length of an 

 entirely septate specimen, incomplete at both extremeties, 3.50 

 inches ; breadth at the larger end, about 3 inches. 



It is possible this may be a larger distorted specimen of the same species as 

 the last, but with the specimens we have yet had for comparison, we cannot do 

 otherwise than regard them as distinct. The form now under consideration 

 differs from C. curtum, so far as we have been able to determine, in not being 

 flattened on each side, and in having its lines of growth passing straighter 

 around, instead of deflected downwards on the sides. Like the last, it can only 

 be referred provisionally to the genus Cyrtoceras, from the typical species of 

 which it differs materially in form. 



Locality and position : Springfield, Illinois; Upper Coal Measures. 



