UNIO. 48} 
Say), Agassiz (1852) : glia, Swainson (1840) (U. ovatus and U. siliquosus) (nee Afglea, 
Leach, 1820) ; Disconaias, Cyrtonaias, Actinonaias, and Amygdalonaias, Fischer & Crosse, 
loc. cit. p. 556, nos. 4, 8, 13, 14 (1893).—Sheli ovate or oblong, smooth, shining; summits 
moderately prominent; ventral margin usually rounded ; cardinal teeth rather strong ; 
posterior lamellz arcuated. 
U. discus, tampicoensis, berlandieri, alienigenus, sapotalensis, computatus, cognatus. 
North America, N.E. and E. Mexico. 
IX, Exurprio, Rafinesque (1820) (U. niger, Raf.=U. cuneatus, Barnes) : Unio, s. str., Agassiz, 
Archiv fiir Naturg. xviii. p. 50 (1852); Cenonaias and Leptonaias, Fischer & Crosse, 
loc. cit. pp. 556, 557, nos. 11, 16 (1893 ).—Oblong, obtusely keeled and angulated behind, 
smooth, solid; cardinal teeth moderate. 
U. tamaulipanus, rubicundus, pliciferus, ravistellus, opacatus, mexicanus, sallei, medellinus, 
eruginosus, radiatulus, rowelli, guatemalanus. 
North America, N.E. Mexico, Guatemala. 
X. Uniomervs, Conrad, Proc. Acad. Phil. 1853, p. 268 (U. declivis and U. camptodon, Say) : 
Uniomerus and Mesonaias, Fischer & Crosse, loc. cit. p. 556, nos. 9, 10 (1893).— Shell 
oblong, smooth, moderately convex, rather thin; cardinal teeth compressed, lamelliform. 
U. manubius, explicatus. 
North America, Central and S.E. Mexico. 
Anodontina, Schliter (1838), type U. teres, Raf.=U. anodontoides, Lea, differs from 
Uniomerus in having a shorter and stouter cardinal tooth and a thicker shell. 
XI. Merarrera, Rafinesque (1820) (U. alatus, Say), Agassiz (1852) : Symphynota, Lea (part.) ; 
Delphinonaias and Phyllonaias, Fischer & Crosse, loc. cit. p. 555, nos. 1, 2 (1893).— 
Compressed, distinctly winged, both shells grown together in the wing; cardinal teeth 
compressed. 
U. largillierti, paludosus, scutulatus, and, somewhat different by the more elongate form 
and very prominent wing, U. delphinulus. 
N. America, Guatemala and Yucatan. 
These remarks on the subgenera of Unio represented within our limits afford the 
following facts regarding the zoo-geographical distribution of the species :— 
(1) A large number of the species, not only from Mexico, but also from Guatemala, 
are nearly allied to North-American ones and there are no similar forms in 
South America. 
(2) That some subgenera seem to be peculiar to Mexico and Guatemala, without 
analogous forms either in North or South America, and this is also the case with 
the Nicaraguan section Arotonaias. 
(3) That Psoronaias is the only section which is also represented in the northern part 
of South America. 
(4) That the group with close radial sculpture of the summits, as U. dslodon, Lam., 
U. multistriatus, Lea, &c., from Brazil, bas no representative in Central America, » 
so far as at present known. 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, March 1900. 61 
