36 NEW UNIONIDiE, MELANID^, ETC., 



character. The beaks are slightly eroded, but there appears at the tips a slight indica- 

 tion of undulations. The angle of the umbonial slope causes a well-marked furrow on 

 the corresponding line of the interior. The wing in this species does not seem to be 

 connate, as the ligament in this specimen is entirely uncovered, and is perfect the 

 whole length. In young specimens this may be found to be otherwise, as it is with 

 some of our species of Unio and Anodonta. I feel greatly obliged to Dr. Kirk for 

 bringing this interesting species to the knowledge of Malacologists. 



Spatha Nyassaensis. pi. 13, fig. 33. 



Testa subsuleata, elliptica, lentioulari, corapressa, valde ina3quilaterali, antice rotunda, postiee obtuse angu- 

 lata; valvulis crassiusculis ; natibus parvis, vix prominuUs, ad apices minute undulatis ; epidermide 

 rufo-castanea vel luteola, obsolete radiata; margarita purpurescente et valde iridescente. 



Shell subsulcate, elliptical, lenticular, compressed, very inequilateral, round before, 

 obtusely angular behind ; valves somewhat thick ; beaks small, scarcely prominent, 

 minutely undulate at the tips; epidermis reddish chestnut color or yellowish, ob- 

 scurely rayed ; nacre purplish and very iridescent. 

 Proc. Acad. Nat. Sci., 1864, p. 109. 



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



My cabinet. 

 Diam. -5, Length 1-2, Breadth 2 inches. 



Shell subsulcate, elliptical, lenticular, compressed, very inequilateral, round before 

 and obtusely angular behind ; substance of the shell somewhat thick ; beaks small, 

 very slightly prominent, minutely undulate at the tips ; ligament long, thin and dark 

 brown ; epidermis reddish chestnut color or yellowish, obscurely rayed and with dis- 

 tant marks of growth ; umbonial slope depressed and rounded ; posterior slope very 

 narrow; elliptical and raised into a , e rp carina; anterior cicatrices distinct, very 

 large and well impressed ; posterior cicatrices distinct, large and slightly impressed ; 

 dorsal cicatrices well impressed and placed in the centre of the cavity of the beaks ; 

 cavity of the shell very shallow and very wide ; cavity of the beaks scarcely percep- 

 tible ; nacre purplish and very iridescent. 



Remarks. — The description is made from a mature, well characterized specimen 

 with the beaks decorticated. Quite a young specimen accompanied it, which I think 

 is of the same species, but still it may belong to another. This has a yellowish epi- 

 dermis and a white nacre. The soft parts were dried in this, but were not perfect 

 enough after softening in water to make out any of its anatomy. I could not ascer- 

 tain if it had the two syphons which designate the genera Iridina and. Spatha. It 

 may really belong to the genus Anodonta. Nyassaensis is near in outline to S. ruhens 

 Lam., but is more oval, approaching an obovate outline. It is also more lenticular 

 and is a much smaller species. It differs also in outline from an African mussel de- 



