﻿*EXOTIC UNIONIDiE. 261 



and do not shew any undulations, but the two young ones have delicate, nearly 

 parallel undulations running from the tip obliquely on the posterior slope, and the 

 anterior slope has also a few indistinct ones. One of the two specimens from Mr. 

 Cuming is marked from " Rio Macacu, Brazil," but I think this must be an error. It 

 is not likely that the same species should exist in the rivers of South America and 

 Africa. This species cannot be confounded with An. arcuata, Fer., which is a 

 ponderous arcuate species from the Nile, although in some characters it resembles 

 that shell. The Senegalensis is more transverse, of a darker green and less ponderous. 



Anodonta Dahomeyensis. PL 41, fig. 141. 



Testa laevi, transversa, subinflata, ad latere cornpressa, ad basim emarginata, valde inaequilaterali ; valvulis 

 tenuibus ; natibus subprominentibus ; epidermide tenebroso-oliva, striata, eradiata ; margarita cseruleo- 

 alba et iridescente. 



Shell smooth, transverse, somewhat inflated, compressed at the side, emarginate 

 at base, very inequilateral ; valves thin ; beaks somewhat prominent ; epidermis dark 

 olive, striate, without rays ; nacre bluish white and iridescent. 



Anodonta Dahomey ensis, Lea. Proc. Acad. Nat. Sci., 1859, p. 154. 



Hab. — Dahomey, West Africa. Mr. Frazer. 



Cabinet of Mr. Cuming. 

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



Shell smooth, transverse, somewhat inflated, compressed at the side, emarginate at 

 base, very inequilateral, obtusely angular behind; dorsal and basal lines nearly parallel ; 

 substance of the shell thin ; beaks somewhat prominent ; ligament long, thin and light 

 brown; epidermis dark olive, transversely striate, without rays, with somewhat 

 distant marks of growth ; umbonial slope somewhat raised and much rounded ; 

 posterior slope raised into a small keel and having one slightly impressed line on 

 each valve from the beaks to the posterior margin ; anterior cicatrices large and 

 distinct, the inferior one being very large in proportion and transverse ; posterior 

 cicatrices rather large and confluent ; dorsal cicatrices single in each valve, deeply 

 impressed and placed nearly in the centre of the cavity of the beaks ; cavity of 

 the shell rather deep and somewhat rounded ; cavity of the beaks very shallow and 

 subangular ; nacre bluish white and iridescent. 



Remarks. — A single specimen only has been submitted to me by Mr. Cuming, and 

 this with very much eroded beaks, so that nothing can be said in regard to the 

 character of their undulations, if they have any. It is always to be regretted to be 

 compelled to make a diagnosis from a single specimen, as has sometimes been done in 

 this paper. Some of the characters mentioned may not be persistent with specimens 

 from different habitats and of different ages or sexes. This should always have con- 

 sideration by the student of natural history. This species is closely allied to Senegalensis 

 herein described, but it differs in several characters. It is larger and rounder over the 



