306 



Physa (Physella) globosa, and not be used in the generic sense 

 for many of the North American forms. The anatomy is still 

 unknown, the two specimens of the original series are the only 

 ones that have ever been found. 



Haldeman's name Physodon (1843, p. 39) and its emendation 

 by Baker is untenable for subgeneric use as the main character 

 for which the name was established, on the presence of columellar 

 teeth, is not a constant character at all and at best can only 

 be considered of specific value. An examination of several 

 hundred specimens from one locality of P. microstoma the type 

 of Physodon, shows this character to be present in only a com- 

 paratively few individuals. Specimens of this species from other 

 localities are entirely without the character. 



Anatomically, there seems to be no justification as yet, to 

 split this genus into groups worthy of generic or subgeneric 

 headings other than P. globosa and P. zionis. By this is meant 

 the forms that are normally associated with P. fontinalis (Linne) 

 of Europe and P. heterostropha (Say) of North America. The 

 elaboration of mantle digitations in Physa fontinalis (Linne) 

 does not, in my opinion, constitute sufficient grounds to separate 

 all North American forms when this same character, though 

 less developed, in the American forms is stated by Baker (1928, 

 p. 409) to be 'not constant enough to furnish criteria for specific 

 determination.' Emendations of previous names, especially 

 when such are not based on the original material are prone to 

 lead to serious errors. Observations made by different authors 

 on the same material or the same species adds materially to the 

 sum of knowledge, but assumptions with no supporting facts 

 lead to trouble and confusion. The emendations made by Baker 

 cannot validate these names when their establishment in the 

 first place was based, as with Physella, upon a species, the shell 

 of which is absolutely different from all other Physas and with 

 Physodon upon a character inconsistent within the species itself. 



The subgenus Alampetis was proposed by von Martens 

 (1898, p. 368) the type selected being P. osculans Hald. (first 

 species under this name in his monograph), though he specifically 

 mentions P. ancillaria Say as belonging to this subgenus as well. 

 The main character upon which this subgenus was erected was 

 that of a smooth surface as compared with a glossy surface as 



