GASTEROPODA OF THE LOWER. GREEN MARLS. 159 



them identical, I have taken them as they are identified and labeled in the 

 collection Acad. Nat. Sci., Phila., and partly from his descriptions. In his 

 comparisons mader A. ovoidea he says that species can be distinguished from 

 this one by "the proportionate length of the mouth, and narrowness of the 

 body whorl, and the acute upper edge of the whorl." The proportional 

 length of the mouth is nearly as given in his description, i. e., less in this 

 one. The volutions are more acute also in that one, while the proportional 

 diameter of the body volution of the two species is very nearly the same 

 in both. The width of the aperture is also greater here than in A. ovoidea; 

 in these respects they nearly agree with his statements. The author 

 remarks that in this species {A. cretaced) there are two folds on the colum- 

 ella," the upper one heavy and rounded, lower or anterior one obsolete." 

 If the lower one is obsolete, which it certainly is in the specimen here used, 

 which is one of the types, it can not exist; therefore there is only one, and 

 not two as he describes. In the other species a similar error is made, as to 

 the relative size of the folds as the anterior one is barely distinguishable 

 on the specimen, which is also one of those used in the original description. 

 Mr. Gabb also states that on one of the casts of this species "the colum- • 

 ellar edge of the body whorl" "is marked by acute angular striae, one 

 branch extending directly upwards on the outside of the whorls [inside of 

 the shell], and soon becomes obsolete; the other branch runs into the 

 columellar cavity." This feature I can not understand, as the specimen is 

 not before me, but I think that by some accident the description in this 

 connection has become mutilated in the printer's hands, and has escaped 

 notice in proof-reading. In remarks below the description he states that 

 from a cast of the surface he believes the exterior to be smooth. As it 

 appears tliat I have not seen all the specimens used by the author, I have 

 retained the name of the species and its identity, thinking it probably may 

 be satisfactorily identified at some future time. 



Formation and locality: In the Lower Grreen Marl at Crosswicks, New 

 Jersey. Collection Acad. Nat. Sci., Phila. 



