496 PROCEEDINGS OF THE ACADEMY OF [1896. 



has since been tested to be singularly well judged. It was a splen- 

 did piece of work, considering the time and material available. 

 But Tryon himself, in his later years, saw as clearly as anyone that 

 a vastly greater reduction of species must be made. He told me, in 

 1888, that, as he now saw these shells, there were not more than a 

 tenth as many good species as names. Whether the particular 

 ratio mentioned was deliberately said or not, I do not know : but I 

 incline to the belief that it will prove near the truth. 



These shells must be collected and studied by river-systems ; and 

 it then appears that often the same species occurs in some localities 

 sculptured throughout, in others only on the upper portion, while 

 in still other places only the earlier whorls may show the character- 

 istic sculpture. Some of the species described from one or two 

 decollate examples will be recognized with great difficulty, if at all, 

 in cases where the type locality is not known. 



A cursory glance at the generic scheme in current use reveals 

 some inaccuracies which call for correction. The genera are un- 

 equally related, and, as Tryon has shown, fall into three main 

 groups. They are as follows : 



lo Lea, 1831, type Fus^is fluvialis Say. Melafusus Swainson, 

 1840, is a synonym. 



LiTHASiA Hald., 1840, type Anculosa (Ldthasia) geniculata 

 Hald. 



A section of Lithasia is Angitrema Hald., 1841, type Melania ar- 

 migera Say; Glotella Gray, 1847, same type, being a synonym of 

 Angitrema. 



It will be observed that this reverses Tryon's usage, as he places 

 geniculata in Angitrema, and restricts Lithasia to smooth species. 



Angitrema is a connecting link between lo and Lithasia, and 

 seems conchologically about intermediate between the two groups. 



Pleukocera Ratinesque, 1818, type? 



Synonyms: Ceriphasia Swains., 1840, type, C. sulcata Swains. 

 (=P. canaliculatum Say); Trypaiiostoma Lea, 1862, type 31. canal- 

 ieulata Say, Teleseopella Gray, 1837, type Melania undulata Say. 



Strephobasis Lea, 1861, types S. spillmani, cornea and clarhii Lea 

 (all =plena Anth.), is a section o^ Pleurocera. 



Elimia H. & A. Adams, 1854, type M. acutocarmata Lea. 



Synonyms : Melasma H. & A. Adams, Juga H. & A. Adams, 

 Megara H. & A. Adams, and Goniobasis^luea,, 1862. 



The group of Adams brothers, Elimia, contains incongruous ele- 

 ments, although most of the species named are Goniobases. E. ele- 



