i3» 



Cincinnati Society of Natural History. 



the shell. The greatest transverse diameter is in the lower 

 half of the body chamber. The siphuncle is marginal on the 

 straight or ventral side, and abruptly expands in the cavities 

 of the short air chambers to two and a half or three times its 

 diameter at the septa. The aperture is unknown. 



The external shell is thin, transversely wrinkled and 

 smooth. The surface being smooth, the transverse wrinkles 

 do not appear as lamellose lines of growth, nevertheless the 

 wrinkles may mark stages of growth in the shell, though they 

 do not conform to the septa or sutures. 



This species does not resemble Gomphoceras eos from rocks 

 of about the same geological age. Gomphoceras eos is longi- 

 tudinally ovoid, but not transversely ovoid. This species is 

 not longitudinally ovoid, for the lateral sides are flattened, the 

 ventral side nearly straight or slightly convex and the dorsal 

 side convex, but transversely it is more or less ovoid. 

 Gomphoceras eos has proportionally a much shorter and more 

 robust bod) r chamber, more numerous air chambers and more 

 arcuate septa, and the siphuncle is eccentric in the middle of 

 the greater diameter of the shell. We have a good specimen 

 of Gomphoceras eos, having eight body chambers, and will 

 give some measurements for comparison. The body cham- 

 ber is i x 8 o% inches long ; 2 T % inches in diameter dorso- 

 ventrally or through the siphuncle ; and 2>-fih inches in 

 diameter laterally ; the length of the eight air chambers is 

 iyVo" inches, making the total length of the entire specimen 

 3 t 5 q°q- inches ; the lateral diameter of the last or eighth 

 air chamber is 2 T W inches, and dorso-ventrally nearly 2 

 inches, though it is broken on the siphuncular side so the 

 latter measurement is not accurate. The specimen illus- 

 trated has a body chamber i-nfV inches long; inches 

 in diameter dorso-ventrally ; and only 2 inches in diameter 

 laterally ; the length of the two specimens does not differ 

 very much ; but the eighth air chamber in the specimen illus- 

 trated has a dorso-ventral diameter of inches and a 

 lateral diameter of only IjJq inches. The outer shell and 

 aperture of Gomphoceras eos are unknown, but our cast shows 

 a deep notch at the ventral side of the aperture, which 

 indicates that the species here described is not congeneric 

 with it. 



