178 PROCEEDINGS OP THE ACADEMY OF 



cus. There are also some differences in the details of the septa, which cannot 

 however, be readily explained without figures. It is likewise much larger than 

 the specimen represented by Dr. Owen, or any individuals of that form we have 

 seen, its length being 4-57 inches ; height 3-87 inches, and its breadth 2*53 

 inches. 



Locality and position. On Yellow Stone River, 150 miles above the mouth, in 

 the upper part of formation No. 4 of the Nebraska Cretaceous Series. 



GASTEROPODA. 



Aporrhais paeva, M. & H. Shell small, conical, subfusiform ; spire moder- 

 ately elevated, and acute at the apex ; volutions six or seven, separated by a 

 small but rather distinct suture, and having around the middle a single series 

 of very oblique, flexuous folds, or node-like costse, which do not extend to the 

 suture either above or below ; last whorl having just below the row of nodes, 

 a small but well defined revolving angle ; surface marked by very obscure 

 lines of growth, and fine, closely set, revolving striae. Length about 0-28 inch ; 

 breadth of body whorl, 0-15 inch ; apical angle a little convex, divergence 33. 



Locality and position, same as last. 



Aporrhais sublevis, M. & H. Shell conical, or subfusiform ; spire elevated ; 

 volutions seven or more, convex, and separated by a rather distinct, though 

 not deep suture ; last one convex above, and abruptly contracted below, having 

 a (single ?) small, revolving angle, which passes around to the suture, but is 

 not seen on the succeeding turn above. Surface polished, and marked by 

 moderately distinct, arcuate lines of growth, which are crossed by rather ob- 

 scure revolving lines, nearly equalling the spaces between, on the spire, but 

 more distant, with sometimes a few indistinct, irregular, very fine, parallel 

 striae between on the body whorl ; aperture and lip unknown. Length about 

 0-54 inch; breadth of body whorl, 0-26 inch; apical angle slightly convex, 

 divergence 37. 



Locality and position. Yellow Stone River, Upper part of No. 4, Nebraska 

 section. 



Dentaliom pacperculum, M. & H. Shell small, arcuate, slender and taper- 

 ing gradually ; section circular ; substance comparatively thick ; surface 

 smooth, but showing under a magnifier extremely fine, obscure lines of growth, 

 which pass around somewhat obliquely. Length (of an incomplete specimen, 

 measuring from the apex,) 0-36 inch; diameter of same at apex 0-03 inch, do. 

 at larger extremity 0-06 inch. 



Locality and position. Moreau River, formation No. 5 of the Nebraska section. 



Cylichna scitula, M. & H. Shell small, rather thick, narrow, subelliptical, 

 or subcylindrical ; spire entirely hidden ; summit truncate, and occupied by a 

 comparatively large umbilicoid depression ; aperture very narrow, moderately 

 arched, and equalling the greatest length of the shell ; umbilical region 

 slightly impressed ; inner lip reflexed upon the columella, which seems to be 

 slightly twisted, so as to form a small indistinct fold at its base ; surface 

 marked by fine, obscure lines of growth, which are crossed by impressed, re- 

 volving striae, separated by spaces about twice or three times their own 

 breadth, near the middle of the outer whorl, but becoming much more closely 

 crowded towards the extremities. Length 0-24 inch ; breadth 0-14 inch ; 

 widest part of aperture 0-07 inch, breadth of same near upper extremity, only 

 002 inch. 



Locality and position. Moreau River, No. 5 of the Nebraska section. 



CONCHIFERA. 



Teredo selliformib, M. & H. Shell small, subglobose ; posterior side nar- 

 rowly rounded above, gaping, and having a broad, more or less angular notch 



[May, 



