102 TVINCHELL AND MARCY ON FOSSILS FROM THE 



eter of the shell. The ventral sinus projects nearly as far as the most prominent portion 

 of the shell on the ventral side ; and is bounded laterally by the two projecting lips of the 

 aperture. The siphon is of medium size, strongly moniliform, situated on the greater axis, one 

 eighth that axis or less, from the ventral side. The septa are deep, regularly concave ; the 

 penultimate chamber is one sixth the depth of the chamber of habitation. Surface of casts 

 marked by numerous incremental ridges, which are deeply sinuate on the ventral side. 



Length of last two chambers, 1.6 inch ; greatest transverse diameter, 1.09 ; greatest 

 dorso-ventral diameter, 1.16; depth of penultimate chamber, .20; dorso-ventral axis of 

 the aperture, .84 ; transverse axis, .60 ; diameter of siphon, .09 ; distance from ventral side, 

 .16.; concavity of penultimate chamber, .18. 



This unique and elegant, and rather abundant species is amply distinct from anything 

 known to us. There is indeed no other with which it can be compared, though it approaches 

 nearest to Gomphoceras pyriforme Sowerby. 



Lituites Breynius. 

 Lituites Hercules W. and M. 

 Plate III. figure 9. 



Shell very large, apparently forming less than a complete whorl in any of the specimens 

 seen. Dorsum and sides flattened-convex — the latter less flattened than the dorsum. 

 Septa moderately concave, plane, much flatter in the middle than around the margins ; si- 

 phon rather small, central. Greatest transverse diameter three fourths the distance from 

 the dorsal to the ventral side, causing the lateral surfaces to approximate dorsally. 



Surface ornamented only by encircling stride which at intervals aggregate into irregular 

 undulations. The strife curve backwards on the sides and make a further deep retral sinus 

 across the dorsum. 



Dorso-ventral diameter, 4.25 inches; transverse diameter, 4.12 ; diameter of siphon, .22; 

 depth of dorsal sinus of the striae, about one inch. The diameter of the shell from the 

 mouth to the opposite side was from seven to nine inches. 



One of our specimens is an impression of the shell in the rock. This shows that the 

 apex of the whorl presented an obtuse termination more than an inch in diameter. 



Cyrtoceras Fosteri Hall, (Wis. Rep. 1861, p. 41). The specimens in our collection enable us 

 to add to Prof. Hall's description the following characters : Shell rather more rapidly ex- 

 panding toward the aperture, which is sinuate on the dorsal side. The exterior is marked 

 by incremental lines, which, on the dorsum, are correspondingly sinuate. The two diame- 

 ters of the aperture in one of our specimens are 1.22 and 1.5 inch ; depth of the last cham- 

 ber, measured on the side, 1.12 ; depth of the apertural sinus, .18. Siphon cylindrical, 

 .07 inch in diameter, where the septa are at the same distance apart. 



Gtkoceras H. de Meyer. 



Gyroeeras Bannisteri W. and M. 



Shell consisting of about one and a half whorls, barely in contact, gradually increasing 

 in diameter; transverse section nearly circular; surface ornamented by encircling convex 

 rido-es which extend quite around the shell, crossing the ventral side at right angles, thence 

 archino - backwards to the dorsal side, where the corresponding branches meet in a broadly 



