[89] 



■where it forms a strong white tubercle, upper lip tooth trans- 

 verse, and opposite to the external periphery ; base convex, um- 

 bilicate, grooved within the umbilicus. Yellowish horn color. 



Diam. 11 — 15, height 6 — 7 mill. 



North Carolina ; vicinity of Philadelphia, Pa., (small variety). 

 Distinguished immediately from tridentata and fallax by its nar- 

 rower umbilicus and groove, and especially by its tubercular 

 basal tooth. See description of T. fallax. 



4. Triodopsis Hopetonensis, Shuttleworth. 



Plate- 9, figure 9. 



Depressed, thin, ribbed-s'triate ; spire obtusely convex, but 

 not much elevated, suture distinct ; whorls 5J, somewhat convex, 

 more convex beneath, constricted behind the aperture ; aperture 

 trilobate, a sharp parietal tooth and a small submarginal one on 

 the upper and the lower lip ; narrowly umbilicated. Light horn 

 color. 



Diam. 13, height 6 mill. (Var. major.) 



Sullivan's Island, S. C. ; Hopeton and St Simon's Isle, Geo. ; 

 Florida. 



Distinguished from fallax by its smaller umbilicus, less 

 thickened lip and teeth, and by the latter being more remote, 

 one from another. The dimensions given above are those of a 

 large specimen; ordinarily they attain but two-thirds of the 

 size. 



5. Triodopsis Yucantanea, Morelet. 



Plate 9, figure 17. 



Shell depressed, almost flat above, but quite convex below the 

 angular periphery; whorls five, obliquely ridged above and 

 striate beneath, constricted behind the reflected lip ; aperture 

 trilobate, parietal tooth very oblique, nearly V-shaped, with one 

 lip tooth opposite to it, and a smaller erect one upon the centre 

 of the basal portion of the lip; umbilicus rather wide and deep. 

 Light horn color. 



Diam. 8, height 3 mill. 



Isle of Carmen, Yucatan. 



