01 
the outside of the shell when the animal is extended, whereas in the 
American forms only the digitate edge is partly reflected over the columellar 
and parietal regions. The name chosen for the American group was Halde- 
man’s Physella founded on a small species, globosa , living in the Nolichucky 
river in Tennessee. 
In a recent paper (1930, page 305) Mr. William J. Clench, who is 
making a special study of this family, questions the use of Haldeman's 
Physella for the American Physas. Its type, globosa, is a small species, 
although adult, and its peculiar environment suggests that it may be 
different from all the other American species and may be closely related to 
Pilsbry’s Petiophysa zionis (Pilsbry, 1925) in which there are no mantle 
digitations. Should this prove to be the case, Physella would constitute 
another monotypic group like Petrophysa. The writer has contended 
that, should Physella be found untenable as a name for the American forms, 
Physodon Haldeman would be available. This provision was mentioned 
in the Wisconsin Monograph. Clench does not believe that this name is 
tenable because the original diagnosis is based on a character, the tuber- 
culate columella, which is not uniformly represented in the type species, 
microstoma, and is not found in the other species included in the genus. 
But this objection is not valid and is not sustained by the International 
Code. If we were to adhere to such a rule we would have to reject about 
half of the ancient genera and subgenera which have been amended by 
later authors, Pilsbry, Dali, Walker, etc., and are received without question 
by modern taxonomists. Most ancient group names have departed a long 
way from the characters given in the original diagnosis. Therefore, as 
Physodon is the earliest name given to a group of American Physas 
its use either as a genus or subgenus name is perfectly regular under the 
code and was properly chosen as a group name by me in the Wisconsin 
Monograph. 
As to the use of Alampetis v. Martens, 1898, this is open to the same 
objections as Physodon, as noted by Clench himself, the characters assigned 
being a smooth and not a glossy shell, characters found in several forms of 
American Physas in the same species, and the group name is no more 
tenable than Physodon. Alampetis may be found to cover peculiarities of 
some of the southern species, Physa osculans being the first species men- 
tioned by v. Martens, who cited no type. Physa ancillaria and P. heteros- 
tropha are mentioned as belonging to the group. 
Whether the American species should be separated from the European 
Physa as a genus or as a subgenus depends wholly on the viewpoint of the 
individual student using the group. The senior author has favoured the 
separation into distinct genera, but it may be best to use these names as 
subgenera, at least until more is known about the genitalia of the European 
species, which, as in the case of Planorbis, may show very definite generic 
characters when more carefully examined. 
The names proposed for the American species of Physa may, therefore, 
be tabulated as follows: 
Physa Deep, 1801. Type: Bulla fontinalis Linn. 
Subgenus Physodon Haldeman, 1843. Type: Physa microstoma Hald. 
Synonvmn: Alampetis v. Martens, 1898. Type: Physa osculans Ilald. 
Subgenus Physella Hald., 1843. Type: Physa globosa Hald. 
Subgenus Petrophysa Pilsbry, 1925. T} r pe: Physa zionis Pilsbry. 
