Ill 



NOTE ON THE LINGUAL DENTITION OF THE 

 STREPOMATID^.* 



As lingual dentition has been adopted as a very 

 important character (somewhat hastily, I think) in 

 the classification of the Mollusca, it may be well to 

 ascertain how far "it may be corroborative with other 

 differences in the genera of North American Strep- 

 omatldce. Troschel, in his magnificent work "Das 

 Gebiss der Schnecken," divides the Melanicms into 

 several groups, of which the following contain Amer- 

 ican species: 



Ancyloti. The peculiarity of the dentition of the 

 forms belonging to this group is that the Rhachidian 

 tooth is broader than long, rounded behind, and 

 swollen out before [auscjebuchtet). The laterals 

 have a rhombic form with the outer posterior angle 

 somewhat drawn out, and the inner Uncini always 

 possess a smaller quantity of denticulations than the 

 outer ones. The jaw exhibits numerous small scales 

 which appear of a polygonal, mostly hexagonal form. 



In this group are included AncijJotus, Melania 

 depygis {Goniohasis) , Gyrotoma and lo. 



We copy the figure given by Troschel : — 



Fig. 17. Ancylotus jyi'cerosus. Fig. 20. Melania depygis. 

 " 18. " costatus. " 21. Gyrotoma ovoidea. 



" 19. " dissimilis. " 22. lo spinosa. 



It will be noticed, by an inspection of these 

 figures, that the differences in the form of the denti- 

 tion are so slight as to be of no value for the pur- 

 pose of separating the genera. Indeed Troschel 

 acknowledges that he can find no difference of sufii- 



♦Froni American Journal of Coucholosj', ii, 134, 18GG. 



