CEPHALOPODA. 333 



GOMPHOCERAS CAMMARUS, n. Sp. 

 PLATE — SUPPLEMENT. 



Shell large, exogastric. The chamber of habitation and five attached air-cham- 

 bers do not show evidences of any decided curvature in the shell. Trans- 

 verse section broadly oval ; lateral diameter the longer. In a longitudinal 

 section the dorsal side is nearly straight, and the ventral side very convex. 

 Point of greatest gibbosity posterior to the outer chamber, at about the fourth 

 septum. Apical angle unknown. 



Chamber of habitation small, with a length equal to about three-fourths of 

 the lateral diameter at the last septum. Dorsal side nearly straight ; ventral 

 side convex, and sloping rapidly to the aperture. Lateral faces convex, regu- 

 larly sloping to the aperture, which is slightly expanded at the lateral mar- 

 gins. The crenulations form a broad, coarsely furrowed band at the base of 

 the grand chamber, having a width of eleven mm., and showing about three 

 transverse furrows in the same space. 



Aperture longitudinally semi-oval, having a length equal to that of the 

 grand chamber. Transverse or ventro-dorsal diameter nearly two-thirds 

 that of the lateral The small aperture is indicated by a deep, broad bend 

 in the margins of the large aperture. Large aperture elliptical, with a 

 ventro-dorsal diameter equal to one-half the lateral diameter. 



Air-chambers regular, having a depth of nine mm. where the tube has a 

 diameter of ninety mm. The last air-chamber has a depth of one-half the 

 adjacent one, and both care shallower than the preceding chamber. Septa 

 smooth, so far as observed, and deeply concave. Sutures straight and 

 horizontal. 



Siphuncle unknown. 



The test on the chamber of habitation is strong, having a thickness of two 

 mm. Surface marked by regular, fine, lamellose lines of growth. 



The internal mould of the specimen, as preserved in a fine, compact, cherty 

 limestone, has the greater part of the test and septa dissolved, giving to 

 the air-chambers an imbricating appearance. The crenulated band is distinct 



