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-chainbers. 
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 
