FRESHWATER AND LAND SHELLS. 33 



by being more regularly elliptical, and being smoother and polished. 

 The nacre of Zeiglerianus, in several specimens before me, is pur- 

 ple and salmon, some having a white margin. I presume the domi- 

 nant colour to be purple. I have pleasure in dedicating this shell to 

 F. Zeigler, a distinguished zoologist of Vienna. 



Unio creperus. Plate X. fig. 28. 



Testa subelUptica, transversissima, valdhin(Bquilaterali; valvulis subcrassis ; natibus pro- 

 minulis, undulatis; epidermide viride; dentibus cardinalibus parvis ; lateralibus vix cernendis ; 

 margarita alba. 



Shell subelliptical, very transverse, very inequilateral ; valves somewhat thick ; beaks 

 rather prominent and undulated at tip ; epidermis greenish ; cardinal teeth small ; la- 

 teral teeth obscure ; nacre white. 



Hab. Tennessee. Professor Troost. 



My Cabinet. 

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



Shell subelliptical, subemarginate at base, very transverse, very ine- 

 quilateral, somewhat flattened over the umbones; substance of the 

 shell thick anteriorly, thin and iridescent posteriorly ; beaks rather ele- 

 vated, retuse, and finely undulate at tip; ligament long; epidermis 

 dark green and obscurely rayed ; cardinal teeth small and elevated ; 

 lateral teeth obscure, being perceptible only at the termination ; ante- 

 rior cicatrices distinct; posterior .cicatrices confluent; dorsal cicatrices 

 In the centre of the cavity of the beaks ; cavity of the shell deep ; 

 cavity of the beak small ; nacre white. 



Remarks. — I owe to the kindness of Professor Troost the single 

 valve which I possess of this species. It has some resemblance to the 

 U. emarginatus (nobis), but perhaps resembles more the U. iris (nobis). 

 In the structure of the teeth, particularly in the lateral tooth, the cha- 

 racter is obscure. In this it resembles the U. calceolus (nobis). At 

 the termination of the ligament there is, however, in my specimen, a 



VI. — 1 



