[88] 



placed an oblique tooth, and small marginal teeth are on the 

 upper and the basal portions of the labrum respectively ; base 

 convex, umbilicus open and deep. Horn color. 



Diam. (large var.) 23, height 9 mill. ; (small var.,) diam. 13, 

 height 5-5 mill. 



Inhabits all the States east of Rocky Mountains. 



This shell is generally larger than the next, from which it 

 diflFers in having a more depressed form and much smaller teeth. 



2. Triodopsis fallax, Say. 



Plate 9, figure 12. 



Shell convex, spire somewhat elevated, suture distinct ; whorls 

 5, moderately convex, obliquely coarsely striate ; aperture trilo- 

 bate, the parietal lamelliform tooth large and oblique, the lip 

 teeth large and flattened, the upper one deflected into the aper- 

 ture ; base moderately convex, umbilicus open. Light horn 

 color. 



Diam. 11, height 6 mill. 



Inhabits the whole country east of Rocky Mountains. 



This shell, as mentioned under the description of T. tridentata, 

 difl"ers from that species by its smaller size, more elevated spire 

 and larger teeth ; the upper lip tooth is remarkable, being quite 

 large, somewhat blade-shaped, and its surface bent into the 

 aperture. I regard this shell as fallax, in deference to the 

 opinions of Messrs. W. G. Binney, Blan,d, &c., but the fact is 

 that Say confounded two species under this name, and his 

 description is actually drawn up from a specimen of introferens, 

 var. minor, as fallax is not found in the vicinity of Philadel- 

 phia — the habitat given by Say. 



3. Triodopsis introferens, Bland. 



Plate 9, figure 5. 



Depressed, thin,, with rib-like striae ; spire convex, but slightly 

 elevated; whorls 5 — 6, somewhat rounded, the last descending, 

 constricted behind the lip, with exterior pits marking the posi- 

 tion of the lip teeth within the aperture, periphery subangular ; 

 aperture trilobate, parietal tooth oblique, lamelliform, basal lip 

 tooth submarginal, lamelliform, continued within the aperture, 



