OF CONCHOLOGY. 279 



UNIO, Retzius. 



4. Unio uber, Conrad. — Plate 15, fig. 16. 



Description. — Bounded, profoundly ventricose; posterior 

 slope with a shallow subangular groove; posterior margin 

 direct, extremity emarginate; umbo broad, inflated; epider- 

 mis brown above, pale olivaceous posteriorly and towards the 

 ventral margin ; within white, teeth very prominent. 



Inhabits the Alabama River. 



This species has some resemblance to a horse-chestnut. 



5. Unio fontanus, Conrad. — Plate 15, fig. 13. 



Description. — Oblong, sub-compressed, thin in substance; 

 disks flattened in the middle; beaks slightly raised above the 

 hinge-line, undulated, decorticated; anterior margin regularly 

 rounded ; posterior extremity sub-truncated, or obtusely round- 

 ed ; color green above, yellowish below and on the posterior 

 slope, rays fine or linear, close, disappearing on the lower 

 part of the anterior side ; umbonal slope undefined ; posterior 

 slope with a slight oblique groove and raised line and distinct 

 green ray; within bluish, white on the ventral submargin; 

 lateral teeth single in both valves. 



Inhabits a rivulet near Vicksburg, Miss. 



I obtained one specimen only of this small species. 



6. Unio prasinattjs, Conrad. — Plate 15, fig. 14. 



Description. — Trapezoidal, very inequilateral; beaks decor- 

 ticated, not plicate, hardly raised above the hinge-line; umbo- 

 nal slope subangulated; posterior margin obliquely truncated, 

 extremity subangulated; color olivaceous, with numerous 

 close green rays, tinged with salmon-color; lateral teeth recti- 

 linear. 



Inhabits Florida. 



