272 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. 

 Placentae 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 

 or red. 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). 19 



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 a rather 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. 



