m 



138 



LAND AND FRESri-WATER SHELLS OF X. A. [PART II. 



Haldeman says " llie teolli are present when the shell is a line 

 in length, and as but one set exists in full grown individuals, we 

 must infer that they are absorbed and reproduced from time to 

 time. In overgi'owu specimens like those figured, it sometimes 

 happens that the teeth are wanting ; as if, after their absorption, 

 the energies of the animal were too far exhausted to reproduce 

 them. The outer ones seem to be formed successively from left 

 to right, the small one on the right appearing last, and in its 

 absence, the shell has been described by Say and Gould as being 

 but five-dentate." 



Ranges from the Eastern through the Middle, Western, and 

 Northwestern States, and as far noi*th as Peace River. 



Subfamily AXCYLIX.E. 



Shell non-spiral, conical, limpet-like. 



All the knowm genera of Ancylinse are represented in Xorth 

 America except Latia, which has a spiral shell and a transverse 

 septum in the aperture. 



Fig. 230. 



AXCYLUS, Geoffroy. 



Tentacles triangular, mantle included ; pulmonary 

 orifice protected by a branchial appendage. Foot 

 large. 



Shell sinistral, thin, patelliform, depressed, non- 

 spiral, apex directed to the right ; aperture very 

 wide ; peritrcmc continuous, simple, entire. 

 Jaws three, covered with papillae, one superior, small, trans- 

 versely oblong, two lateral, long, very slightly arcuate, contiguous 

 to the superior. 



