96 



of tbe shell. Umbilicus covered. Epidermis light green with faint red revolv- 

 ing bands. 



This shell most resembles V. subpurpurea, but is easily distinguished 

 by having six whorls, which are much narrower than in that species. The 

 spire is almost double the length of that of subpurpurea, and the epider- 

 mis is lighter in color. 



V. subsolida, Anthony. Proc. Acad. Nat. Sci. p. 71, 1860. 



Through the kindness of Prof. D. S. Sheldon, of Davenport, Iowa, I have 

 received a number of specimens of this shell and of V. i n t e g r a , Say, from 

 ^.he Mississippi River at that place. The latter reaches the size of s u b s o 1 i d a, 

 which it much resembles, but it is easy to separate them by the following dis- 

 tinctive characters : 

 V. subsolida. 



Spire longer than the aperture, consisting of seven whorls, acuminate. 

 Body whorl subangulated near the middle, the angle being quite conspicu- 

 ous in half-grown shells. 

 V. integra. 



Spire shorter than the aperture, consisting of six or occasionally six and a 

 half whorls. Body scarcely angulated, being almost regularly convex. 

 Shell much more ventricose than subsolida. 



V. ponderosa, Say. 



May be readily distinguished from V. i n t e g r a by its shorter spire, much 

 more ventricose form, and by the body whorl being almost flat in the centre, 

 so that its lateral sides for some distance are almost parallel. The shoulder 

 of tbe wtorls is also more prominent than in either of the other specimens. 



AMNICOL1DJE, Tryon, 1862. 



AMNICOLA, Gould and Haldeman. 



There are two very distinct groups of shells included by authors in this 

 genus • in the first, which may be considered typical, the shells are globose, 

 with a' short spire of three or four whorls ; the second I propose to separate as 

 a subgenus, which may be thus characterized : 



Subgenus Pomatiopsis, Tryon, 1862. 



Shell elongate, the spire (of about six whorls) much exceeding the length 



of the aperture. 



Example. A.lapidaria, Say. 



A. depresea, Tryon. 



T. orbiculata, subbyalinii ; anfractibus quarternis, convesis; 

 ultimo magno, 5 — 6 totius longitudiuis asquante, anguste umbilicata. 

 Apertura, semi-circulari ; labio interne appresso. Sutuia impressa. 

 Long. 4 mill. Lat. 4 mill. 

 (Figure magnified 1\ times.) 



Hob. — Mississippi River at Davenport, Iowa. Prof. Sheldon. 

 Coll. Acad. Nat. Sci., Smithsonian Inst., and of Prof. D. S. Sheldon, Isaac 

 Lea, J G. Anthony, and Geo. W. Tryon, Jr. 



Shell subhyaline, rather solid, orbicular ; spire depressed, consisting of near- 

 ly four whorls; apex acute, suture profoundly impressed. Body whorl very 

 convex equalling 5-6ths the total length of the shell, narrowly umbilicate. 

 Aperture semi-circular, the inner lip being nearly straight. 



The only shell which this resembles is V. subglobosa, Say, which is, 

 however double the size of A. depressa, with a rather more exserted spire, 

 and more concave inner lip. 



