CEPHALOPODA. _ 459 



been observed. The convexity of the saddle is about equal to the depth of 

 the chambers at the umbilical margin ; and where the distance of the septa 

 at their origin is four mm., they are distant about seven mm., as measured 

 from the summits of the adjacent saddles. The suture-lines, so far as pre- 

 served, are delicately marked on the flattened surface of the compressed 

 specimen. Siphuncle undetermined. 



The test is only preserved in a macerated and exsolute condition, and in 

 some parts covering the cast with a thin film, or leaving the surface-markings 

 impressed upon the interior. The surface-markings, as preserved, and as 

 impressed upon the matrix consist of regular sublamellose strise, which are 

 about .5 mm. distant, but become crowded upon some parts of the surface. 

 The striae are gently curved backward from the umbilicus, making a broad 

 curve over the lateral face of the volution ; thence advancing toward the 

 aperture, as they approach the exterior margin, they make a sudden retral 

 bend over the periphery, forming a deep sinus in the ventral side. As the 

 stria? approach the periphery, and become recurved upon that portion of the 

 shell, they are much stronger. The form of the sinus is undetermined. 



The internal cast is extremely flattened, preserving the impressions of the 

 surface striae and the suture lines. The greatest diameter of the specimen 

 figured, which is probably a little increased by pressure and distortion, is 

 about eighty mm. 



This form has a very close general resemblance to G. complanatus, and the 

 surface striae are of precisely the same character, and have the same course 

 and direction, except that the shallow, undefined groove, on the lateral face 

 near the periphery, has not been observed. The umbilicus is entirely open, 

 as in that species, and the proportions of the inner volutions are similar ; but 

 the outer one is more rapidly expanding, and embraces a greater proportion of 

 the inner volution. The septa, how.ever, in this form have a much greater 

 proportional distance. This feature alone should be regarded as distinctive, 

 when compared with the same on the specimen, fig. 8 of pi. 70. 



Formation and locality. In the lower beds of the Portage group, at Homer, 

 Cortland county, N. Y. 



