PRESHWATEU AND LAND SHELLS. 25 



a yellow brown, and in this stage indistinct rays may occasionally be 

 observed. The general colour of the nacre seems to be white, with 

 a disposition to pinkish in the teeth. Sometimes this colour extends 

 over the whole of the thick parts of the nacre, which is very pearly ; 

 a tint of salmon colour, in some individuals, may be observed in the 

 cavity of the shell and beaks. The dorsal line in the specimen before 

 me, is slightly tuberculated in an irregular manner. 



Unio Cumberlandicus. Plate VII. fig. 19. 



Testa elliptica, transversa, incequilaterali ; vahulls tenuibus ; natibus prominuUs ; epider- 

 mide lutea, radiata ; dentibus cardinalibus parvis ; lateralibus longis rectisque ; margaritd 

 alba et iridescente. 



Shell elliptical, transverse, inequilateral ; valves thin ; beaks somevi'hat prominent ; 

 epidermis yellow, radiated; cardinal teeth small; lateral teeth long and straight; na- 

 cre white and iridescent. 



Hab. Cumberland River, Ten. Professor Troost. 



My Cabinet. 



Cabinet of Professor Troost. 



Diam. -5, Length -8, Breadth 1*5 inches. 



Shell elliptical, transverse, inequilateral, umbonial slope rounded ; 

 substance of the shell thin, thicker before ; beaks somewhat promi- 

 nent; ligament short; epidermis yellow, with numerous nearly equi- 

 distant rays ; cardinal teeth small, double in the left valve, and disposed 

 to be bifid in the right; lateral teeth long and straight; anterior cica- 

 trices distinct ; posterior cicatrices confluent ; dorsal cicatrices placed 

 in the centre of the cavity of the beaks ; cavity of the shell rather 

 shallow ; cavity of the beaks small ; nacre white, and very iridescent 

 behind. 



Remarks.—! owe this shell to the kindness of Professor Troost. It 

 most resembles U. iris (nobis), and may easily be mistaken for that 

 species. It differs in being less transverse, in being more yellow and 

 in having fewer rays. 



VI. G 



