CHIEFLY OF THE UNITED STATES. 323 



which cover the whole disk ; umbonial slope low and rounded ; posterior slope raised 

 into a carina; anterior cicatrices confluent, large and very slightly impressed; 

 posterior cicatrices confluent, large and very slightly impressed ; dorsal cicatrices 

 invisible; cavity of the shell rather shallow; cavity of the beaks shallow and 

 obtusely angular ; nacre blue, very thin. The dorsal edge thickened and slightly 

 curved upward at the anterior end. 



Soft Parts— K single female, and probably not half-grown. Ova were found in the 

 ovarium, but none in the branchial uterus. Branchiae small, inner ones much the 

 larger, rounded below, united the whole length of abdominal sack. Palin small, 

 rounded below and subangular posteriorly, united only above. Mantle very thin, 

 thickened and colored at the edges. Branchial opening rather small, dark on the 

 edges, with rather coarse papilte. Anal opening very small, with a few small 

 papillfB, the edges being united below. Super-anal opening rather large, the edges 

 being open below with the anal opening. Color of the mass whitish. 



Remarlis.—K single specimen only of this species was received in alcohol by the 

 Smithsonian Institution from Dr. Strebel. I am kindly permitted by Prof Henry, 

 Secretary of that admirable Institution, to describe this and Unio Veracruzensis, and 

 it gives me great pleasure to call it after Dr. Strebel, who took it from the fresh 

 waters near Vera Cruz. In outline it is nearly allied to An. undulata, Say, but 

 differs in being a thinner species, in not having any callus under the hinge, and 

 being covered with beautiful capillary rays over the whole disk. The beaks are not 

 perfect enough to display any undulations, if there be any belonging to the species. 



Unio prunoides. PL 53, fig. 136. 



Testa Itevi, elliptica, valde ventricosa, insequilaterali, antice et postice rotundata ; valvulis subcrassis, 

 antice aliquanto crassioribus ; natibus prominulis ; epidermide tenebroso-fusca, eradiata ; denti- 

 bus cardiualibus compressis, obliquis et valde crenulatis ; lateralibus longis, lamellatis corru- 

 gatisque; margarita argentea. 



Shell smooth, elliptical, very ventricose, inequilateral, rounded before and behind ; 

 valves rather thick, somewhat thicker before ; beaks somewhat prominent ; epidermis 

 dark brown, without rays ; cardinal teeth compressed, oblique and very much crenu- 

 lated ; lateral teeth long, lamellar and corrugate ; nacre silver-white. 

 Proc. Acad. Nat. Sci. 1868, p. 150. 



Hah. — South America? 



Cabinet of the Academy of Natural Sciences. 

 Diara. 1-1, Length 13, Breadth 2 inches. 



Shell smooth, elliptical, very ventricose, inequilateral, rounded before and behind ; 



76 



