22 



RESEARCHES TPON THE HYDROBIIN.!; 



the others gradually decreasing in size outwardly, the outermost 

 being obtuse and rather a lobe than a denticle. Intermediate 

 tooth with the body perforated/ and the peduncle more than twice 

 as long as the body ; cusp 1-denticulated, the third denticle 

 (counting from within) being twice as broad as the others. 

 Inner lateral tooth with fourteen denticles at the summit. Outer 

 lateral also with fourteen denticles. 



Mr. A. 0. Currier, of Grand Rapids, Mich., has obligingly 



sent me, from that locality, alcoholic specimens of the 



Melania isogona of Say (Fig. 12), placed in Amnicola 



by Dr. Lea, which may prove to be congeneric with 



Somatogyrus depressus. Among these specimens there 



were fortunately some male individuals, so that the 



character of the verge could be determined. This organ (Fig. 



13) is here much compressed, and bifid, 



the inner branch being much longer 



than the outer, but no longer than the 



basal part ; while the outer is short, 



somewhat triangular and pointed, and 



contains the canal, which is conspicuous 



from its white color. The rostrum in 



the same species is rather broad, flat, 



and square-cut ; the tentacles are rather 



short, in their contracted state scarcely longer than the rostrum, 



and flattened. 



In the lingual dentition of S. isogonus, of which a figure is 

 here given (Fig. 14), with a more enlarged view of the rha- 



Fig. 13. 



Fig. 14. 



' It is very difficult to determine, with the instruments at my command, 

 whether the liole seen iu the figure is a true perforation, or only a deep 

 pit. It certainly has the appearance of lieing the former, though, if so, it 

 is liard to say what its office can be. Nothing like it has yet been de- 

 scribed by Troschel or any oilier author. 



