CHIEFLY OF THE UNITED STATES. 321 



cicatrices confluent and very slightly impressed ; dorsal cicatrices placed in the cavity 

 and on the under side of the plate ; cavity of the shell shallow ; cavity of the 

 beaks very shallow and subangular; nacre bluish, passing into pink at the teeth. 



Soft parts. — Probably a young male ; a single specimen, Bratichice small and very 

 thin, inner one much the larger, rounded below and united the whole length of 

 abdominal sack. Paljii small, elongate, oval and united only above. Mantle very thin, 

 slightly thickened at the edges. Branchial opening rather large, with numerous, 

 small papillse on the inner edges, which are nearly black. Anal opening very small, 

 with numerous, very small papillse on the inner edges. Super-anal opening rather 

 large and united below. Color of the mass white. 



Remarhs. — A single specimen, in alcohol, only was received, in the " envoi " of Dr. 

 Strebel, and this probably only half grown. In outline it is near to Medellinus (nobis), 

 from Mexico, but still nearer to subangulatus (nobis), of Georgia. The specimen before 

 me has rays over the whole disk, but they are indistinct, and this may arise from its 

 being a long time in alcohol. It is probable that old specimens would be without rays. 

 The teeth of this specimen are pinkish and old specimens, if the nacre be thick, are 

 likely to have the whole interior more or less pink or purplish. The beaks are eroded 

 and do not present any undulations, which may exist at the tips. 



Unio Ortonii. pi. 52, fig. 134. 



Testa plicata, lato-elliptica, compressa, valde insequilaterali, postice angulata, antice rotundata ; valv- 

 ulis crassis, antice crassioribus ; natibus prominulis ; epidermide rufo-fusca, eradiata ; dentibus 

 cardinalibus multipartitis, flexuosis curtisque ; lateralibus prelongis, curvatis corrugatisque ; mar- 

 garita albida et valde ifidescente. 



Shell folded, widely elliptical, compressed, very inequilateral, angular behind and 

 rounded before ; valves thick, thicker before ; beaks slightly prominent ; epider- 

 mis reddish-brown, without rays ; cardinal teeth much divided, bent and short ; 

 lateral teeth very long, curved and roughened; nacre whitish and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 161. 



Hob. — River Napo, Equador, Prof Orton, 



Cabinet of Smithsonian Institution. 

 Diam. 1"6, Length 3-1, Breadth 5'3 inches. 



Shell folded, widely elliptical, compressed, very inequilateral, angular behind and 

 rounded before ; substance of the shell thick, thicker before ; beaks slightly promi- 

 nent; ligament long and thick; epidermis reddish-brown, without rays; umbonial 

 slope raised and furnished with five or six rather distant irregular folds ; posterior 

 slope raised into a sharp carina ; cardinal teeth much divided into eight or nine 

 curved denticles, the anterior one being much the larger; lateral teeth very long, 



