16 rafinesque's 



94 Sp. Unio pallens, (Obliq. ditto. 1821.) Shell thick com- 

 pressed, perfectly elliptic, both ends equal, hardly subtruncate 

 behind, outside smooth pale yellowish, inside white. Length 3-5, 

 diameter 3-10, axis 1-5 of the breadth. 



Ohio and Kentucky, rare, 2 or 3 inches. Lamellar tooth a little 

 obliqual, short and thick, in the left valve furrow closed as in the G. 

 Obovaria and Rotundaria. Yet an Elliptio which is the same as 

 Ellipsaria. 



95 Sp. Unio rivularis, (Obliq. ditto. 1821.) Shell rather thick 

 swelled, perfectly elliptical, slightly arcuate below, outside brown 

 and smooth, inside, bluish. Length 4-t, diameter 3-7, axis 2-7, of 

 breadth. 



In the small streams of the Knob-hills and Cumberland mountains. 

 Very small, hardly one inch. Lamellar tooth as in sp. 93. — Near 

 to U. sinuata, sp. 67. 



96. Unio fontinalis, (Obliq. ditto. 1823.) Shell thick, rounded, 

 triangular, svib-truncate behind ; quite rounded before and below ; 

 outside smooth, yellow, with some green spots ; inside bluish white. 

 Length 4-5, diameter 3-5, axis 2-5 of the breadth. 



At the spring of the source of Green R. in the Knob-hills, rare, 

 very small, like a Cyclas ; but belong to S. G. Scalenaria, lamellar 

 tooth obliqual, straight, short. 

 [4] 



97 Sp. Unio chJoris, (Obliq. chloris. 1823.) Shell oval obliqual, 

 rather thick, and swelled ; the 3 sides rounded, outside greenish and 

 smooth, inside bluish iridescent. Length 4-5, diameter 3-5, axis 1-5 

 of the breadth. 



Small streams of Knob-hills. Minute shell, next to U. calendis 

 Sp. 89, but distinct, lamellar tooth more curved, and not bisulcate. 

 Both are Sintoxia. 



98 Sp. Unio castaneus ; [Obliq. and Aximedia, 1823.] Shell 

 rather thin, oval, elliptical, swelled, nearly equilateral, broader be- 

 hind, outside very smooth, and chesuut colour ; inside, bluish white. 

 Length 4-5, diameter 3-5, axis 3-7 of the breadth. 



Knob-hills streams, in east Kentucky. — Yery small, lamellar tooth 

 suboblique, thin. Perhaps a variety of U. lenigata. Sp. 9. 



G. Truncilla. 

 , 99 Sp. Unio j^ierplexus. (Tr. perplexa, 1830.) Shell rather 

 ubov'al, slightly swelled, only subtruncate ; rounded below, outside 



