1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 319 



The following is a list of genera which I place in this family : 



Unio, Ketzius. 



Anodonta, (Brugui^re em.) Lamarck. 



Frisodon, Schumacher. 



Tetraplodon, Spix. 



Castalina, v. Iheriug. 



Burtonia, Bourguignat. 



Arconaia, Courad. 

 Cristaria, Schuiuacher. 

 Lepidodesma, Simpsou. 

 Fseudodon, Gould. 

 Leguminaia, Conrad. 

 Solenaia, Conrad. 



Family MUTELID.E. 

 Genus MUTELA, Scopoli.' 



As yet, we know very little of the anatomy of this or several other 

 groups of African Naiades, and upon shell characters alone it seems 

 difticnlt to decide whether this should be united with Spatha or kept 

 separate. Typically the shells are quite distinct; those of Mutela 

 being thin, elongated, and often furnished with quite well-developed 

 taxodont teeth; while those of Spatha are solid, oval or oblong in out- 

 line, and have only a low, compressed tubercle or short ridge on the 

 hinge line. But there are species which are so completely intermediate 

 that it is very difficult to say to which group they belong. Most of them 

 have unusually soft, brilliant nacre, generally inclining to bluish in the 

 characteristic Mutelas, and to coppery in the Spathas. According to 

 Clessiu,^ the mantle lobe of Mutela is united as far as the middle of the 

 ventral margin; the animal has two stout siphons, and the shell gapes 

 in front. Fischer states^ that the palpi are long, curved and rounded 

 at their extremities, and that the external branchijie are united to the 

 mantle throughout. Adams Brothers'* say that in Mutela the inner gill 

 is entirely united to the foot, while in Spatha it is free. If this distinc- 

 tion could be proved to be good throughout, it would be a sufficient 

 character on which to base the two genera, but in Unto it is well known 

 that the union of the inner gill with, or its separation from the foot, or 

 the connection of the outer gill with the mantle, is very variable. 



Mutela dubia, Gmelin, shows two or more slightly compressed eleva- 

 tions on the hinge line, especially in the left valve, and sometimes 

 smaller denticles, while in ^[. exotica, Lamarck, the Avhole hinge line 

 is often strongly crenulated. 



The name Mutelhia, which was proposed by Bourguignat'"' as a genus 

 to include Anodonta senegalensis^ Lea, and Mutela roHtrata, liang, is 

 synonymous with Mutela and Spatha. 



'Intr. Hist. Nat., p. 397, 1777. 



^Kuster, Couch. Cabinet, IX, 1. Abth., p. 191. 



3 Man. de Couch., p. 1004. 



^The Genera of Recent Mollusca, II, pp. 505-507. 



^Esp. nouv. et gen. nouv. des grands Lacs Africains, p. 488, 1885. 



