lOO LAND AND FRESH WATER MOLLUSKS 



^Costatella Dall, Ann. Lye. N. H. N. Y., ix, p. 355, 1870. Type Physa 



costata Newcomb. 

 "^Costella Meek, Inv. Fos. Upper Missouri, pp. 603-604, 1876 ; lapsus pro 



Costatella. 

 '^Macrophysa Tryon, Struct. Syst. Conch., iii, p. 103, 1884. 

 .ff«//««j Westerlund, Fauna Pal. Reg., p. 54, 1885 (not of Adanson, 1757) ; 



Acta Acad. Sci. Slav. Merid., Zagrabiae, cli, p. 119, 1902. 

 <^BuUinus Oken, Lehrb. d. Naturg., sp. x, 302-3, 181 5. B. fontinalis L., 



first species. 



This genus has suffered from its resemblance to the sinistral Lym- 

 naeas and the physiform Planorboids, which have been and still are 

 frequently confounded with the true Physas. Not until much more is 

 known of the dentition and soft parts will it be practicable to eliminate 

 from Physa all the unrelated species. The group containing Isidora^ 

 Physopsis^ etc., is chiefly South European and African, but it is 

 probable that some of the subtropical American species also belong to 

 it. The subgenus Physella Haldeman, was proposed because the 

 author believed it to be branchiate instead of pulmonate, but we now 

 know that undoubted species of LymncBa^ having no access to the 

 atmosphere, live in the deep waters of some of the Swiss lakes, per- 

 haps gathering up globules of oxygen freed by aquatic plants ; and 

 unless some more definite observations show anatomical distinctions 

 (such as were merely surmised by Haldeman) the group is hardly 

 worth retention. Physodon Haldeman, so far as the shell is concerned, 

 differs from Physa s. s. only by an almost imperceptible thickening 

 below the obscure plait on the pillar, and, in default of other charac- 

 ters, might well be dispensed with. 



The soft parts of Diastropka contorta (Mich.) have not been de- 

 scribed, and there is some reason to think it may be an Isidora. Gray, 

 who first introduced it in connection with the above mentioned species, 

 subsequently listed it as a name (MS. .?) given by Guilding, and men- 

 tioned as type Physa guildingi Swainson, which is an Aplexa. 



The groups into which the genus may confidently be divided are as 

 follows : 



Section Physa s. s. Shell sinistral, ovoid, polished, with a spire shorter 

 than the length of the aperture, an obscure plait on the pillar, with 

 the pillar merging gradually into the peristome, the outer lip sharp, 

 often with a slight thickening internally, the inner lip closely 

 appressed to the body and pillar, a very small or no umbilicus, the 

 surface of the shell smooth or microscopically striated. Type Bulla 

 fontinalis Linn^. Holarctic and Temperate regions of both hemi- 

 spheres, also Hawaii. 



