704 UNIO 
doubt the lobe of the mantle fills the hollow spines until it has 
reached its full height, when it closes up the outer end and 
in retreating fills the cavity solid or nearly so. One shell in 
the Lea collection shows a spine broken off at the point where 
it bifurcates and each part of the spine is hollow. The surface 
of the shell is bright and usually rayed. One of Lea’s shells 
has beautiful, dark, broad. blotched rays, which become nar- 
rower below as if the dark color had been poured on at the 
beaks and had run down the sides of the shell. It also has a 
few detached blotches. 
Notwithstanding the remarkable character of well-developed 
spines on the only species of this group, U. spinosus, the animal 
even when gravid does not present any striking peculiarities, 
and is certainly a Unio. 
Mr. Charles FE. Svkes, of Gardia, Georgia, in a letter written 
to me, states that he found this species in the Altamaha River 
about 15 miles above tide water in limited numbers, where they 
usually burrow in white sand where there is running water 
from two to four inches deep. 
Section Unromerus Conrad, 1853. 
Uniomerus Conran, Pr. Ac. N. Sci. Phila., VI, 1853, p. 268.— 
Ortmann, Ann. Car. Mus., VITI, 1912, p. 272. 
Shell trapezoid, with a rounded posterior ridge, and pointed 
or feebly biangulate behind; beaks not prominent, sculptured 
with to to 15 curved, rather strong, concentric ridges, which 
sweep decidedly upward behind, where they are drawn some- 
what closely together ; epidermis generally rayless, often cloth- 
like; pseudocardinals usually compressed; laterals delicate, 
slightly curved; muscle scars large, shallow; nacre generally 
lurid. 
Animal with the marsupium occupying the whole length of 
the outer branchiz, pad-like; gills large, inner the larger, free 
nearly or quite the length of the abdominal sac; mantle gen- 
erally rather thick, thicker and double on the edge. 
Type, Unio tetralasmus Say. 
Ortmann, (1. c.), raises this group to generic rank. 
