258 VALLONIA. 



a deep suture ; the last comparatively narrow, little expanding 

 toward the aperture, descending in front. Aperture very oblique 

 and inclined, transversely, short ovoid or oblong ; peristome solute, 

 continuous, shortly everted, except near the suture, without a lip. 



Alt. 0'7, greater diam. 2'0, lesser T7 mill. 



Knoxville, Tennessee; Jackson Co., Alabama; Iowa (drift on 

 Missouri river.) 



Jaw slightly arcuate with fine, irregular ribs slightly denticulat- 

 ing the cutting edge. Kadula with 77 transverse rows of 25 teeth ; 

 of the 5 laterals the fifth has a small, though distinct, plate and the 

 ectodont double pointed ; on the sixth, or first marginal, the outer 

 cusps are only 2-3, comparatively large. 



The free, continuous peristome (see fig. 45) is a character distin- 

 guishing our species from all others known to me. In general the 

 aperture is not as conspicuously elongated transversely as in other 

 related forms, and the inner part in some examples is at least as 

 well rounded as the outer, or even more (fig. 44). There are about 

 35 ribs on the last whorl, as there are also in V. parvula, which the 

 present species resembles in size and general appearance ; but the 

 wider umbilicus, the transversely elongated aperture, continuous 

 peristome, the absence of a strong lip, and the last whorl descending 

 in front, are sufficient to distinguish the form under consideration. 

 From its small size, coloration and the ribs, V. perspectives forms a 

 remarkable contrast to the other large species of the group, with 

 which it is yet connected by the configuration of the apertural parts. 

 It might just as well be placed in a separate group. 



V. TENUILABRIS A. Br. Type unfigured. 



Shell with umbilicus open and rapidly widening at the aperture, 

 depressed convex, with prominent almost papilliform apex, with fine 

 and acute crowded ribs ; grayish horn colored. Whorls 4-4, some- 

 what convex, the last somewhat expanding in front, gradually deeply 

 descending ; suture rather impressed. Aperture very oblique, little 

 crescentic, transversely oval-rounded with margins much approx- 

 imate, peristome everted [widened], thinly lipped, yellowish horn 

 colored, inferior margin reflected. 

 . Alt. 1-7-2, diam. 3 mill. (Braun.) 



Siberia; Jarzowa, Selo, at 60 10', and Werschininsky, 58 55'; 

 fossil in southern Germany. 



