204 DESCRIPTION OF 



laminae of the epidermis which give the whole disk (except at the beaks) a 

 rough appearance. The epidermis is lighter about the beaks. 



Unio tortivus. Plate 12, Fig. 17. 



Testa ellipticd, compressd, emarginatd; valvulis subtenuibus; natibus subprominentibus, compressis ; 

 epidermide tenebroso-fuscd, striatd; dentibus cardinalibus parvulis; lateralibus longis curvisque; raar- 

 garitd purpurea et iridescente. 



Shell elliptical, compressed, emarginate; valves rather thin; beaks somewhat prominent, compressed ; 

 epidermis dark brown, striate; cardinal teeth very small; lateral teeth long and curved; nacre purple and 

 iridescent. 



Hab. Chattahoochee River, Columbus, Georgia. Dr. Boykin. 



My Cabinet. 

 Diam. .6, Length .1, Breadth 1.9 inches. 



Shell elliptical, compressed, emarginate at base; substance of the shell rather 

 thin; beaks somewhat prominent, compressed; ligament rather long and thin; 

 epidermis dark brown, striate; cardinal teeth very small and lobed; lateral teeth 

 long and curved; anterior cicatrices distinct; posterior cicatrices confluent; 

 dorsal cicatrices placed in the centre of the cavity of the beaks; cavity of the 

 shell very shallow; cavity of the beaks very shallow; nacre purple and irides- 

 cent. 



Remarks. — This species belongs to that group of which the U. compla- 

 naUts, may be considered the type, the nacre of which is usually purple, 

 but sometimes white and salmon. The four specimens which are before me 

 have all more or less purple, one being deeply coloured with it and tinged with 

 purple, while another is almost white. It differs from the complanatus in being 

 more compressed and in having a very small cardinal tooth. It is also a 

 much smaller species. At the posterior margin there is a disposition to bi- 

 angulation. 



Unio lenior. . Plate 12, Fig. 18. 



Testa obovatd, inflatd; valvulis tenuibus; natibus vix prominentibus, ad apices undulatis; epidermide 

 luted, densissime radiatd; dentibus cardinalibus compressis; lateralibus parvis ; margarild alba et iri- 

 descente. 



