Die ANNALS OF THE CARNEGIE MUSEUM. 
Posterior margins of palpi connected for a short distance. Inner 
lamina of inner gills free, except anteriorly. 
Both of my specimens are gravid, but have only eggs. Marsupium 
formed by the outer gills, only moderately swollen, with sharp edge. 
Placenta moderately well developed. 
Hinkley collected these specimens in December and January. Here 
we would have a so-called ‘‘summer breeder,’’ which breeds in mid- 
winter. But we know now, that not the season of the year, but the 
shortness of the breeding season is important, and according to all 
analogies, E. popei should be a form with short breeding season. 
Genus UNIOMERUS Conrad. (1853.) 
Conrad, 1853, p. 268.—Simpson, 1900), p. 739 (as section). 
Shell moderately elongated, with straight longitudinal axis, not 
oblique, and beaks not very near the anterior end. Beaks not very 
prominent, beak-cavities shallow, hinge-teeth well developed. Outer 
surface without. sculpture. Epidermis light yellowish to brown, 
often with dark concentric bands, without rays. Beak-sculpture 
rather distinct, concentric, bars rather numerous, not angled behind, 
but curved up toward the posterior side of the beaks, and not parallel 
to the growth lines. Nacre whitish or grayish, not inclining to purple 
orred. Soft parts practically identical with those of Elliptio. Gravid 
females are unknown, but in sterile females only the outer gills are 
marsupial in structure. The anal has, in the type species, only crenu- 
lations, and the mantle-connection between anal and supra-anal is 
rather long. 
Type U. tetralasmus (Say).¥ 
This genus stands very close to Elliptio, and, like this, may be 
regarded as descended from Pleurobema. 
Uniomerus tetralasmus (Say). 
One male and two females (sterile) from Bayou Pierre, De Soto 
Parish, Louisiana, have been received from L. S. Frierson. 
The soft parts do not offer anything remarkable, when compared 
with those of Pleurobema and Elliptio. The supra-anal is separated 
from the anal by arather long mantle-connection, the latter, however, is 
19 The first species given by Conrad is declivis, which, according to Simpson, 
together with six of the other so-called species named, are synonyms, or varieties, 
of tetralasmus. 
