CEPHALOPODA. 341 



sesses no distinctive features. Crenulated band having a width equal to the 

 distance between the septa, and marked by broad, shallow furrows, which are 

 continued over the cast of the walls of the air-chambers. 



Aperture unknown. 



Air-chambers regular, with a depth of about seven mm., the last one being 

 somewhat shallower than the preceding. Septa smooth and deeply concave, 

 so far as noticed. Sutures straight and horizontal, but little impressed upon 

 the internal mould. 



Siphuncle submarginal, moniliform, exposed in the process of weathering; 

 expanding in the cavities of the air-chambers to twice its diameter at the 

 septa, being nearly equal to the depth of the air-chambers. 



Test and surface-markings unknown. 



Internal mould essentially smooth, with the exception of the crenulations, 

 which are continued over the walls of the chambers. 



The specimen described, embracing a small portion of the grand chamber 

 and eight attached air-chambers, has a length of ninety mm., of which 

 twenty-eight mm. pertain to the outer chamber. 



This species is distinguished by its short, rapidly enlarging tube, the charac- 

 ters of the crenulations, and the position and elements of the siphuncle. The 

 example figured, as preserved in the shales, is considerably compressed, but the 

 characters of the internal mould, the siphuncle and crenulations are distinctly 

 retained. 



Formation and locality. In the shales of the Hamilton group, near Caze- 

 novia, N. Y. 



GOMPHOCERAS LUNATUM, n. Sp. 



PLATE XCV, FIGS. 10-13. 



Shell large, regularly arcuate, exogastric. Transverse section broadly oval ; 

 lateral diameter the longer, and in the ratio of 4 to 3 to the ventro-dorsal 

 diameter. Longitudinal section lunate, with the point of greatest transverse 

 section posterior to the middle of the chamber of habitation. Tube regularly 



