OP CONCHOLOGY. 



51 



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 

 differs 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^\ 

 differs 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, Bland, &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 C€nvex, 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. 



