CHIEFLY OF THE UNITED STATES. 33 



(legans, (nobis,) it has flattened sides, but it is not so rounded at the basal margin nor 

 is it so flat on the posterior slope. In the character of the rajs it differs entirely, 

 elegans having beautiful zig-zag rays over the whole disk, while Kirhii has capillary 

 rays only. In the tripartite character of the lateral teeth it differs entirely. The 

 posterior slope of this species has a beautiful and remarkable posterior slope, the 

 central part being a fine regular well defined ellipse of a dark green, surrounded by a 

 yellowish area, through which on each valve there is a well defined capillary line 

 running from the beak to the posterior basal margin. The folds on the specimen 

 before me are small and delicate, and are only found on the slopes before and behind 

 the beaks and on the points of the beaks. I have great pleasure in dedicating this 

 interesting little species to Dr. Kirk, to whom all malacologists are indebted for the 

 development of the sliells of Lake Nyassa. 



Unio Nyassaensis. pi. 12, fig. .32. 



Testa plicata, triangular!, subinflata, ad latere planulata, laasqullaterall, aatlce rotunJata, postlce angulata; 

 valvulis subcrassis, antlce erassiorlbus ; natlbiis promlnentibus, solldis, ad apices uudulatis ; 

 epidermlde luteo-cornea, obsolete radlata; dentibus cardinallbus parvlusoulis, sulcatis; lateralibus 

 subrectis, curtis, crassls, in utroque valvule duplioibus ; margarita salmonis colore tincta et 

 iridesceute. 



Shell plicate, triangular, somewhat inflated, flattened at the side, inequilateral, 

 rounded before and angular behind ; valves somewhat thick, thicker before ; beaks 

 prominent, solid and undulate at the tips ; epidermis yellowish horn color, obscurely 

 rayed ; cardinal teeth rather small and sulcate ; lateral teeth nearly straight, short, 

 thick, double in both valves ; nacre salmon color and iridescent. 

 Proc. Acad. Nat. Sci., 1864, p. 108. 



Hah. — Lake Nyassa, Central Africa, John Kirk, M. D., of the Zambezi Expedition. 



My cabinet. 

 Diam. -6, Length -9, Breadth 12 inches. 



Shell plicate over most of the disk, triangular, somewhat inflated, flattened at the 

 sides, inequilateral, rounded before and angular behind ; substance of the shell some- 

 what thick, thicker before; beaks ijrominent, solid and undulate at the tips; 

 ligament short and dark brown ; epidermis yellowish horn color, obscurely rayed 

 and with two distant marks of growth; urabonial slope raised and obtusely angular ; 

 posterior slope rather narrow, cordate, somewhat flattened, with an impressed and a 

 colored narrow line from the tips to the posterior basal line ; cardinal teeth rather 

 small, sulcate and much divided ; lateral teeth nearly straight, short, thick and 

 double in both valves ; anterior cicatrices distinct, large and well impressed ; poste- 

 rior cicatrices confluent, rather large and moderately impressed; dorsal cicatrices 

 within and above the cavity of the beaks ; cavity of the shell rather deep and wide; 



