AND DESCRIPTIONS OF NEW SPECIES. 69 



Unio Trapezoides. Plate III. fig. 1. 



Testa trapezia simili, inrnquilaterali, transversa, postice undulatd; valvulis 

 crassis ; dentibus cardinalibus utriusque valvula duplicibus ; lateralibus laminatis 

 curvisque; margaritd purpurea et iridescente. 



Shell trapezoidal, inequilateral, transverse, undulated behind ; valves thick ; 

 cardinal teeth double in both valves ; lateral teeth curved and lamelliform ; nacre 

 purple and iridescent. 



Hab. Lake St Joseph, Louisiana. J. T. Grifiith, Esq. 



My Cabinet. 



Cabinet of Prof. Vanuxem. 



Diam. 1-9, Length 2-6, Breadth 4-3 inches. 



Shell trapezoidal, more angular behind, transverse, undulated on 

 posterior half ; umbonial slope elevated almost into a carina, anterior 

 to vsdiich the undulations are oblique and disposed to lie parallel to 

 each other ; posterior slope large and elevated into a carina ; sides 

 flattened ; substance of the shell thick ; beaks slightly prominent and 

 incurved ; ligament large, long and slightly curved ; epidermis black 

 and w^rinkled ; cardinal teeth double in both valves, crenate and 

 deeply cleft in the left valve ; lateral teeth, long, curved and lamelli- 

 form ; anterior cicatrices distinct and rough ; posterior cicatrices con- 

 fluent ; dorsal cicatrices situated under the posterior part of the cardinal 

 tooth ; ventral cicatrix very perceptible ; cavity of the beaks M^ide and 

 deep; nacre dark purple and iridescent. 



Remarhs. — This highly interesting species came into my possession 

 through the kindness of J. T. Griffith, Esq. of Natchez. It approaches 

 the U. plicatus* of Lesueur, more nearly than any other species with 

 which I am acquainted ; it differs, however, from that species, strik- 

 ingly, in the colour of the nacre, in the general outline of the shell 



* For the authority of this name and author, see Am. Conch, article Unio crassus ; also 

 Barnes's article in Silliman's Journal, Vol. VI. p. 120. 



Vol. IV.— S 



