-MOLLUSOA. 653 
Unio rugosulcatus (p. 522). 
This species is credited to “Central America ” by Simpson (loc. cit. p. 794), without 
hesitation, but also without more precise information concerning the locality; he 
places it in the section Pachynaias, Crosse, of the genus Quadrula, near U. spheniopsis, 
Morelet. | 
Unio metallicus (p. 522). 
See anted, pp. 505 (under U. cuprinus), 650. 
Unio callosus (to follow U. metallicus, p. 523). 
Unio callosus, Lea, Trans. Am. Phil. Soc. ii. p. 31 (1841); Obs. Unionidae, iii. p. 77, t. 23. 
fig. 54°. 
Lea 1? states that this species was obtained from the Ohio Canal, below Columbus; 
but Simpson (Joc. cit. p. 701) says “I am sure that the locality is wrong and it appears 
to be a Mexican form.” If so, I should place U. callosus near U. cuprinus. 
ANODONTA (p. 523). 
Simpson (/oc. cit.), following a hint given by H. v. Ihering, distributes the Unionide 
with toothless hinge, hitherto usually called Anodonta, under two genera, widely separated 
one from the other: Anodonta, s. str., with the embryos in the outer gills, and placed, 
therefore, in the subfamily Unionine, division Homogene; and Glabaris (Gray), with 
the embryos in the inner gills, family Mutelide, most of them South-American. This 
distinction will probably hold good, the geographical distribution of Glabaris extending, 
according to Simpson himself, from the Argentine Republic to the Island of ‘Trinidad 
(G. liotaudi, Guppy), and to the River Medellin in Eastern Mexico (G. cylindracea, 
Lea). As regards the sculpture of the summits, he states that the true Anodonte have 
‘‘numerous more or less parallel ridges, usually somewhat doubly looped,” and that 
Glabaris has the “‘ beaks full, smooth.” This is a character visible also in dry specimens: 
it holds good in the European Anodont@ ; but as to the exotic species it cannot usually 
be ascertained, full-grown examples with worn summits being often only available for 
examination. 
Amongst the Mexican species, the following have waved wrinkles on the summits, 
A. coarctata, A. richardsoni, and A. exilior, which are thus proved to be true 
Anodontew. I have already placed (anted, pp. 524, 525) the Mexican and Central- 
American forms under two groups, one with a small rounded, and one with a deeper- 
pointed, sinulus at the hinder end of the hinge-line; the latter belong to Glabaris, 
according to Simpson, and they have also, so far as I can ascertain, rather swollen 
(full) and smooth summits. This difference in the shape of ‘the sinulus will perhaps 
help to locate the position of full-grown dry specimens with worn summits in the 
