32 NEW UNIONID^, MELANID.E, ETC., 



subtriangular form — Rajaherisis, (nobis,) for instance — and in the subplicate character 

 of some of our southern species, inclining to nodulous. It is greatly to be regretted 

 that none of the soft parts were preserved, that we might compare their anatomy 

 with those from America. Lake Nyassa is one of the three great central lakes of 

 Africa, and has a southern drainage in the Zambezi River. It is, in extent, as Dr. 

 Kirk informs me by letter, " exceeding two hundred miles north and south, and from 

 fifteen to sixty miles wide, and is fifteen hundred feet above the sea. It lies between 

 the parallels of 10° and 14° south latitude." 



Unio Kirkii. pi. 12, fig. 30. 



Testa plicata, triangiilari, subinflata, ad latere plauulata, insequilaterali, autice rotundata, postice anoulata ; 

 valvulis crassis, antics crassioribus ; natibus valde prominentibus, solidis, ad apices undulatis ; 

 epidermide viridi, radiis capillaris indutis; dentibus cardinalibus crassis, sulcatis ; lateralibus sub- 

 vectis, Curtis, crassis, in valvule sinistro tripartitibus ; margarita argentea et irideseente. 



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

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

 prominent, solid, undulate at the tips ; epidermis greenish and covered with capillary 

 rays; cardinal teeth thick, sulcate ; lateral teeth nearly straight, short, thick, and 

 treble in the left valve ; nacre silvery white 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. -7, Length 1-1, ' Breadth 1-2 inches. 



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

 rounded before and angular behind ; substance of the shell thick, thicker before ; 

 beaks very prominent, solid and undulate at the tips ; ligament short, thick and 

 light brown ; epidermis greenish and covered with capillary rays on the sides, and 

 with distant niarks of growth ; urabonial slope raised and angular ; posterior slope 

 flattened, elliptical, yellowish, with a dark green elliptical centre and distinct 

 capillary line on each valve from the beaks to posterior basal margin ; cardinal teeth 

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

 double in the right and treble in the left valve ; anterior cicatrices distinct, rather 

 large and well impressed; posterior cicatrices confluent, rather large and well 

 impressed; dorsal cicatrices placed within the cavity and near the base of the 

 cardinal tooth ; cavity of the shell rather shallow and wide ; cavity of the beaks 

 rather shallow and subangular ; nacre silvery white and iridescent. 



Remarlcs. — This species reminds us at once of an Asiatic and an American species 

 as regards its outline, but having folds on the anterior and posterior slopes it difl'ers 

 from both in this character. It is not so rounded on the basal margin as Rajahemls, 

 (nobis,) nor quite so much inflated, and has not so flat a posterior slope. Like 



