DESCRIPTIVE 
CATALOGUE OF THE NAIADES 
II. 
Genus UNIO Retzius, 1788. 
Unio Rerztus, Diss. Hist Nov. Test. Gen., 1788, p. 16.—Bru- 
GUIERE, Choix de Memoirs, I, 1792, p. 106—ORTMANN, 
mun, Car, Mais, Vili tos. p. 273. 
Limnea Poti (part), Test. Utr. Sic., I, 1791, p. 31. 
Lymnium Oxen, Lehrbuch, 1815, p. 237. 
Elliptio RAFINESQUE, J. de Phys. Nat. Hist., 1819, p. 426. 
Mysca ‘Turron, Conch. Ins. Brit., 1822, p. 243. 
Canthyria Swainson, Tr. on Moll., 1840, p. 278. 
Uniomerus Conran, Pr. Ac. N. Sci. Phila., VI, 1853, p. 268. 
Shell inequilateral, oval to elongated, rounded in front and 
pointed or biangulate behind, with a more or less developed 
posterior ridge, often becoming slightly arcuate when old; 
beaks only moderately full, generally sculptured with coarse 
ridges, which run parallel with the growth lines, or are some- 
what doubly looped, sometimes broken, and showing fine radi- 
ating lines behind; surface smooth, slightly concentrically 
ridged or pustulose; epidermis generally rather dull colored, 
ravless or feebly rayed; hinge plate narrow; two pseudocardi- 
nals and two laterals in the left valve and one pseudocardinal 
and one lateral in the right, with rarely a vestige of a second 
lateral; cavity of the beaks not deep or compressed. Animal 
having the inner branchize free from the abdominal sac for 
from one-half to their entire length; marsupium occupying the 
