480 MOLLUSCA. 
South America. The strongly tuberculated species of Unio forming the subgenera Quadrula 
and Rotundaria, Raf., Agass., Cyprogenia and Tritogenia, Agass., well represented in North 
America, are absent in Mexico. 
II. Psorowaras, Fischer & Crosse, loc. cit. p. 556. no. 6 (1893) : Iridea, Swainson (1840) (part.). 
—Shell with granulated sculpture over the greater part, solid, and with strong cardinal teeth. 
(a) U. semigranosus, psoricus, corium, morint, crocodilorum. (b) Very compressed: U. ostre- 
atus and percompressus. 
Known from N.E. Mexico to Guatemala, absent in North America, represented in the 
northern part of South America by U. yranosus, Brug., from Cayenne. 
II]. Aroronatas, n.—Shell triangular, rather compressed, and of comparatively small size, with 
strong concentric, often somewbat irregular, sculpture and strong teeth. In some species 
the summits are unequal. 
U. cyrenoides, newcombianus, gabbianus, encarpus, caldwelli, imbricatus, granadensis, aratus. 
Nicaragua and Panama. I know no similar forms, either from North or South America. 
IV. Prevropema*, Rafinesque (1820), Agassiz (1852).—Shell solid, triangular or obliquely 
quadrate, often biangulated behind, without peculiar sculpture ; summits prominent ; 
cardinal teeth moderately thick, furrowed and crenulated. 
To this North-American subgenus, near U. rubiginosus, Lea, I refer the Mexican U. couch- 
ianus and the Guatemalan U. spheniopsis and U. usumacinte: Fischer & Crosse (1893) 
propose for each of them a distinct subgenus, viz. Pachynaias for U. spheniopsis, Amphinaias 
for U. couchianus, while U. usumacinte is included by them in Psoronaias. 
V. Spnenonatas, Fischer & Crosse, loc. cit. p. 557. no. 18 (1898).—Shell oblong, cuneiform, 
swollen in the fore part, lengthened and attenuated behind; cardinal teeth rather thick. 
U. liebmanni, acutirostris, goascoranensis, and tehuantepecensis. 
So far as at present known, confined to Mexico, Guatemala, and Honduras. 
VI. Nepuronatas, Fischer & Crosse, loc. cit. p. 556. no. 12 (1893).—Elongated, compressed, rather 
smooth, but not shining; summits much advanced ; ventral margin mostly sinuated, hinder 
end rounded ; cardinal teeth moderate. 
U. aztecorum, popei, poeyanus, from Mexico. The Mexican U, strebeli and the Guatemalan 
U. microdon may also be placed here, although somewhat differing. The North-American 
type of Cunicula, Swains. (1840), U. fasciolaris, Raf. (phaseolus, Hildreth, planulatus, Lea), 
resembles them in several respects. 
VII. Srmonaias, Fischer & Crosse, loc. cit. p. 557. no. 17 (1893).—Shell with distinct concentric 
furrows; oblong or elongated, summits advanced, ventral margin mostly straight ; cardinal 
teeth rather strong. 
U. cuprinus, dysoni, macnieli, yzabalensis, championi, hjalmarsoni, nuculinus. 
S.E. Mexico to Honduras and Nicaragua. 
VIII. Lampstzis +, Rafinesque (1820) (U. cardium, Raf.=U. ventricosus, Barnes, and U. ovatus, 
* Fischer, Manuel de Conch. p. 1000 (1885), incorrectly quotes Uniopsis, Swains. (1840), as a synonym of 
Pleurobema: Swainson, it is true, named U. mytiloides as belonging to it (Malacol. p. 382); nevertheless he 
meant a species without lateral teeth, as is clear by his remarks on p. 289, and by the position he assigns to 
the genus among the Alasmodontine, p. 382. 
+ According to the author, this name is modified from “ Lasma-campsilis, lama flexualis”’ (more correctly 
é\acpa xapiov), a very peculiar contraction indeed. 
