134 AMERICAN JOURNAL 



NOTE ON THE LINGUAL DENTITION OF THE 

 STREPOMATIDiE. 



BY GEORGE W. TRYON, JR. 



As lingual dentition lias 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 Strepomatidie. Troschel, in his magnificent work 

 " Das Gebiss der Schnecken," divides the Melanians into seve- 

 ral groups, of which the following contain American species : 



Ancyloti. The peculiarity of the dentition of the forms 

 belonging to this group is that the Ehachidian tooth is 

 broader than long, rounded behind, and swollen out before 

 (ausgebuchtef). 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 Ancylotus, Melania depygis (Go- 

 niobasis), Gyrotoma, and Io. 



We copy the figures g.ven by Troschel : — 



Ancylotus preerosus. See plate 11, fig. 1. 



costatus. " 11, " 2. 



" dissimilis. " 11, " 3. 



Melania depygis. " 11, " 4. 



Gyrotoma ovoidea. 12, " 1. 



Io spinosa. " 12, " 2. 



It will be noticed, by an inspection of these figures, that the 

 differences in the form of the dentition are so slight as to be 

 of no value for the purpose of separating the genera. Indeed, 

 Troschel acknowledges that he can find no difference of suffi- 

 cient importance for 'the separation of Melania depygis, or of 

 Gyrotoma* from Ancylotus. 



* He curiously regrets that the nearly -allied genus Scliizostoma, Lea, is 

 unknown to him! 



