AND DESCRIPTIONS OF NEW SPECIES. 89 



sent species forms a natural link between Unio and Anodonta, by 

 means of this imperfect lateral tooth. 



Unio Acutissibius. Plate X. fia;. 18 



C5* 



Testa angusto-ellipticd, inaquilatei'ali, postice acute angulatd ; vndulis a clivo 

 umboniali divaricantibus; natibus prominulis; valvuUs tenuissimis; dentibus cardi- 

 nalibus parvis, lateralibus longis reclisque; margaritd tenuissimd, colore salmonis 

 tinctd. 



Shell narrow-elliptical, inequilateral, transverse, acutely angulated behind, with 

 undulations diverging from tlie umbonial slope ; beaks slightly prominent ; valves very 

 thin; cardinal teeth small ; lateral teeth long and straight; nacre salmon-coloured 

 and very thin. 



Hab. Alabama river, Judge Tait. 



My Cabinet. 

 Diam. -4, Length '5, Breadth 1-1 inches. 



Shell narrow-elliptical, transverse, acutely angulated behind, with 

 undulations diverging from the umbonial slope ; substance of the shell 

 very thin ; beaks slightly prominent and placed about one third the 

 distance from anterior margin ; ligament linear ; epidermis yellow, 

 smooth and shining ; cardinal teeth small and single in both valves ; 

 lateral teeth long and straight ; anterior cicatrices distinct; posterior 

 cicatrices confluent ; dorsal cicatrices within the cavity of the beaks ; ca- 

 vity of the beaks wide and shallow, nacre salmon-coloured and very thin. 



Remarks. — This minute shell, among the smallest of the species, is 

 most nearly allied in outline to U. anoilontoides. It differs from it in 

 having undulations, and is totally dissimilar in point of magnitude. 



Vol. IV.— X 



