132 



Probably the specimens before me are immature, bat the 

 species is quite distinct from any other. 



Of Planorbis dentiferus Ad., (Proc. Bost. Soc. Jan. ly 

 1845,) a variety occurs, which is destitute of teeth ! After a 

 careful examination of many specimens, I am unable to find 

 any other differences constantly associated with this peculiar- 

 ity. Many of the toothless shells are more compressed oblique- 

 ly just below the periphery, than the type, but the same is 

 true of some of the shells in which the teeth are well devel- 

 oped. It is not a local variety, both kinds occurring together 

 at Hatfield, in "Westmoreland. The variety may be designa- 

 ted by the name edentatus. 



Ancylus obliquus. Shell subovate, somewhat arcuate, 

 very convex : translucent, pale horn color : extremely thin, 

 with microscopic radiating raised lines, and less distinct striae 

 of growth : apex very prominent, elevated, extending very far 

 to one side and posteriorly, and projecting nearly over the 

 margin. 



Length .075 inch ; breadth .05 inch ; height .028 inch. 



This remarkable shell may belong to a new genus, but 

 without the soft parts, it is difficult to determine the generic 

 value of its peculiarities. The shell is hitherto unique in the 

 rich collection of the Hon. Edward Chitty, to whom I am in- 

 debted for the loan of it. 



Truncatella modesta.' Shell much elongate, ovate conic : 

 yellowish horn color, with a white upper margin of the whorls : 

 with about twenty-one prominent compressed ribs, and nu- 

 merous spiral striae, which are interrupted by the ribs : apex 



truncate with the loss of whorls : spire with the outlines 



somewhat curvilinear : whorls remaining after truncation 

 seven, moderately convex, margined above : aperture subovate, 

 slightly angulated anteriorly. 



