524 MOLLUSCA. 
sinulus, a notch in the hinge-line at the hinder end of the ligament: this, I think, is 
an important character, the sinulus being deep, triangular, with a sharp point, and 
vertically as deep as broad, in the South-American species, and, on the contrary, shallow 
and rounded below in the North-American and European forms. H. v. Ihering has 
pointed out that in the South-American Anodonte the eggs are hatched within the 
inner gills of the mother, whereas in the North-American and European species they 
are hatched within the outer gills: he has also noted that the form of the larva 
(“lasidium ”) of the South-American Anodonte is different from that of the European 
and North-American forms (‘“ glochidium”) (see ‘ Archiv fiir Naturgeschichte,’ 1893, 
pp. 45-140). We may therefore assume that the above-mentioned variation in the 
form of the sinulus coincides sufficiently well with the difference in the development 
to authorize a primary subdivision in this genus; and this is especially important for 
our purpose, as in Central America the Nearctic and Neotropical forms intermingle. 
I propose, therefore, the following subdivision :— 
A. Sinulus shallow, rounded. 
[Palearctic, Nearctic, and Central-American species: none on the mainland of South America. ] 
I. Anopon Ta, s. str.—Summits little prominent or nearly plane, dorsal margin slightly arcuated, not 
distinctly angulated at its fore end; shell moderately convex. Includes the greater part of 
the North-American and Palwarctic species. Fischer and Crosse divide the Mexican and 
Central-American representatives of this section into two subgenera :— 
(a) Brachyanodon, Fischer & Crosse (1893).—Shell rather short, dorsal margin ascending 
posteriorly : A. coarctata, richardsont, exilior, chalcoensis, montezuma. 
(b) Mesanodon, Fischer & Crosse (1893).—Shell oval, dorsal margin less ascending 
posteriorly : A. lurulenta, henryana, tehuantepecensis. 
This separation, I fear, can scarcely be maintained with regard to the numerous North- 
American, or even the European, species, which, apparently, are not subgenerically distinct 
from the Mexican ones. 
II. Gonrpxa, Lea (1870).—Elongated, hinder part of the shell obliquely keeled : 4. angulata, Lea, 
California. 
III. Paruxaria, Swainson, Treat. Malac. p. 381 (1840)*: Pteranodon, P. Fischer, Manuel de Conch. 
p- 1003 (1886) ; Pyganodon, Fischer & Crosse (1893).—Summits very prominent, swollen ; 
shell very convex; dorsal margin distinctly angulated at its fore end, often also at its hinder 
end. Sinulus somewhat deeper, but always rounded. Ventral margin arcuated. Includes 
A. woodiana and A. magnifica, Lea, from China; A. vescoiana, Bourg., from the Euphrates 
River; A. grandis, Say, A. gibbosa, Say, and A. stewartiana, Lea, from Eastern North 
America; A. glauca, from N.W. Mexico; A. globosa, tabascensis, nopalatensis, and 
grijalve, from EH. and S.E. Mexico. 
* Swainson quotes his A. ovata and A. rotundata as typical species of Patularia: the latter is without 
doubt the Chinese A. magnifica; the former either A. glauca, Val., or a nearly allied form. Fischer’s subgen. 
Pteranodon is proposed for the Chinese species. 
