OF CONCnOLOGY. 123 



the only species whicli he cites under the name, are dissimiUs, 

 Say, and turgida, Hald., both carinate shells. I am con- 

 vinced, from studying numerous examples, that the characters 

 of 3Iudalia are not persistent. The globose form of so-called 

 AyicuIosEe, represented by altilis, does not belong to the family. 

 Mr. Gill has proposed for it the generic name Somatogyrus, 

 and it is now included in Amnicolidse. 



These same Virginia and Ohio thin species, together with 

 the dentate forms, compose the subgenus Nitocris, H. & A. 

 Adams, a synonym, anyhow, and otherwise of no value. 

 Mr. Anthony proposes to me to call such shells as 

 Anoulosa vionodontoides ' Spirodon,^ h\it the toothed columella 

 is not even a constant specific character. 



The characters assigned to lo, Pleurocera, Angitrema, Litha- 

 sia, Sirephobasis, Eurycselon, Goniobasis, Schizostoma, Mesechiza 

 and Anculosa, are by no means of equal value. I regard the 

 first five as members of the Trypanostomoid section of the 

 family, of which lo is a genus, with Pleurocera for a sub- 

 genus. Lithasia should, perhaps, be - considered a subgenus 

 only of Angitrema, which is the highest development of this 

 form, having the thickened colum.ella. 



Strephobasis occupies a position between Lithasia and 

 Goniobasis, but I think that it, also, should be considered a 

 subgenus of Angitrema. 



Eurycselon, Gon'obasis, Schizostoma, Meseschiza, and Anculosa, 

 are certainly distinct genera; the first four approximate, form- 

 ing the Goniobasic group or section ; and the last forms a sec- 

 tion by itself, characterized by an entire aperture. 



Yet this arrangement is liable to exception, as all the 

 species of a genus do not fulfill the ideas here conveyed. 

 Some species, on the contrary, remind one of genera which do 

 not immediately succeed or precede them. Moreover, anato- 

 mical researches will enable us probably to separate the 

 natural genera of this family much more sharply than we are 

 now doing, and may enable us to seize on corroborative 

 characters of the shell, which are now overlooked, or whose 

 importance, in this connection, have *been thus far under- 

 estimated. 



