CEPHALOPODA. 351 



GOMPHOCERAS TUMIDUM, n. Sp. 



PLATES XCIII, FIG. 6; XCV, FIGS. 2, 3, 4, 5, 7. 



Shell subglobose, attenuate at the apex. Point of greatest transverse section 

 on the chamber of habitation, posterior to the middle. Tube expanding 

 gradually at the apex, with the sides concave, becoming convex and rapidly 

 inflating over the chamber of habitation. 



Chamber of habitation large, ventricose, with the sides convex, and sloping 

 rapidly to the aperture. 



Air-chambers regular, increasing in depth from the apex, varying from two 

 to three mm. in the length of thirty mm. Sutures straight and horizontal. 



Surface marked by fine striae of growth. 



Internal mould smooth, with the sutures slightly impressed. 



A much compressed specimen, consisting of the chamber of habitation and 

 about sixteen attached air-chambers, has a length of seventy mm., of which 

 twenty-five ram. pertain to the grand chamber. The greatest transverse 

 diameter, in its compressed condition, is forty-five mm. 



This species is distinguished from G. oviforme in the position of the plane 

 of greatest transverse section, the absence of marked crenulations, and the 

 inflated appearance of the greater portion of the tube, with its attenuate apex. 



Formation and localities. In the shales of the Chemung group, near Ithaca, and 

 in the calcareous beds of the upper members of the group, at New Albion, Cat- 

 taraugus county, N. Y. 



GOMPHOCERAS POTENS, n. Sp. 

 PLATE — SUPPLKM BUT. 



Shell large, clavate, robust, exogastric. Dorsal side nearly straight. Ventral 

 side convex. Transverse section broadly oval. Tube regularly and gradu- 

 ally enlarging from the apex. Apical angle 27°. 



Chamber of habitation, aperture, test and surface-markings unknown. 



Air-chambers deep, regularly increasing in depth toward the outer cham- 



