CHIEFLY OF THE UNITED STATES. 291 



Diam. -6, Length 1, Breadth 1'4 inch. 



Shell smooth, subrotund, compressed, inequivalve, inequilateral, rounded, before 

 and behind ; substance of the shell rather thin ; beaks a little prominent ; ligament 

 small and jjale brown ; epidermis transversely' striate, dark green and very much 

 radiated; umbonial slope depressed and rounded; posterior slope subcarinate, 

 narrow elliptical ; anterior cicatrices confluent and somewhat impressed ; posterior 

 cicatrices confluent and very slightly impressed ; dorsal cicatrices placed on the 

 upper side of the cavity of the beaks; cavity of the beaks shallow and rounded; 

 cavity of the shell very shallow and subangular; nacre bluish-white and very 

 iridescent. 



Remarks. — A single specimen only of this species was received. It is closely allied 

 to incequivalva, herein described, in most of its characters, and especially in being 

 inequivalve. It may be distinguished in being more rounded, in being lenticular and 

 in having dark green rays over the whole disk, except on the posterior slope, which 

 is yellow, while the anterior slope is covered with dark green. The nacre is 

 remarkably brilliant. The beaks are eroded and do not seem to possess any 

 undulations. 



Anodonta Bridgesii. pi. 42, fig. 104. 



Testa Ijevi, oblonga, iuflata, iuEequilaterali, antice et postice rotundata ; valvulis pertenuibus ; natibus 

 prominulis ; epidermide Isevissima, micante, olivacea, obsolete radiata ; margarita elegantissime 

 iridescente. 



Shell smooth, oblong, inflated, inequilateral, rounded before and behind; valves 

 very thin ; beaks a little prominent ; epidermis very smooth, shining, olivaceous 

 and obscurely radiated ; nacre elegantly iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 95. 



Sah. — Lake Nicaragua, Central America, Mr. Th. Bridges. 



My cabinet and cabinet of the Academy of Natural Sciences. 

 Diam. 1-7, Length 2-5, Breadth 4-7 inches. 



Shell smooth, oblong, inflated, inequilateral, rounded before and behind; dorsal 

 and basal margins nearly' parallel ; substance of the shell very thin ; beaks a little 

 prominent ; ligament long, thin and light brown ; epidermis very smooth, shining, 

 olivaceous, with very distant marks of growth and obscurely radiate ; umbonial slope 

 rounded ; posterior slope raised almost into a keel, the whole being dark green ; 

 anterior cicatiices distinct, very large and very slightly impressed; posterior 

 cicatrices very large and very indistinct; dorsal cicatrices placed within the cavity 

 of the beaks; cavity of the shell large and wide; cavity of the beaks rather shallow; 

 nacre remarkably brilliant and iridescent. 



71 



