﻿LAMPSILIS 133 



Margarita (Unio) iroostcnsls Lea, Syn., 1836, p. 21; 1838, p. 



18. 

 Margaron (Unio) troostensis Lea, Syn., 1852, p. 25. 

 Margaron (Unio) troostii Lea, Syn., 1870, p. 39. 

 Unio troostii B. H. Wright, Check List, 1888. 

 Unio vanuxemensis Sowerby, Conch. Icon., 1866, pi. xxxix, 



fig. 216. 



A remarkable species, in which the form of the male shell is 

 like that of the female until it is about half grown, when for 

 some reason it begins to be constricted just behind the middle 

 base and becomes much produced behind when adult. 



Lampsilis perpurpueeia (Lea). 



Shell elongate oval or subrhomboid, scarcely inflated, some- 

 times subcompressed, rather solid, beaks in all the specimens 

 seen so badly eroded that no characters could be made out, but 

 probably not very full or high ; surface with irregular growth 

 lines, dark brownish or blackish, darker behind, with feeble, 

 narrow, wavy rays, which show plainly by transmitted light ; 

 left valve with two triangular pseudocardinals and two short, 

 straight laterals ; left valve with three pseudocardinals, the 

 central one strong, the others faint, and one lateral with some- 

 times a furrow on its lower face ; beak cavities shallow, show- 

 ing two or three deep pits ; muscle scars impressed; nacre deep 

 purple, iridescent behind. The male and female shells differ 

 considerably, but not so much as in L. trabalis. The male 

 shell is somewhat drawn out behind and is straight or slightly 

 incurved on the base ; the female shell is irregularly long ovate, 

 faintly incurved behind the feeble marsupial swelling. 



Length (male) 52, height 27, diam. 16 mm. 



Length (female) 55, height 31, diam. 18 mm. 



Tennessee River drainage, extending into Virginia in the 

 Clinch. 



Type locality, Tennessee. 

 Unio pcrpurpureus Lea, Pr. Ac. N. Sci. Phila., V, 1861, p. 41 ; 



Jl. Ac. N. Sci. Phila., VL 1866, p. 46, pi. XVI, fig. 44 ; Obs., 



XL 1867, p. 50, pi. XVI, fig. 44. 



