888 QUADRULA 
double; anterior muscle scars deep; posterior scars distinct; 
nacre lurid whitish, dull. 
Length 65, height 55, diam. 33 mm. 
Type locality, Holston River, Tennessee. 
Quadrula flexuosa Stmpson, Proc. Ac. N. Sci. Phila., 1900, p. 
83, pl. m1, fig. 8; Syn., 1900, p. 790. 
The above form shows relationship to several others, yet 
although I have only seen a single shell, which is in the col- 
lection of Mr. L. S. Frierson, I cannot connect it with any- 
thing else. It is less inflated and more elongated than Q. plena, 
it is less triangular than Q. obliqua and the light-colored epi- 
dermis with the distinct rest marks differs from that of any 
related species: 
QuADRULA PYRAMIDATA (Lea). 
Shell generally, when adult, having the outline of a scalene 
or right-angled triangle, the beaks being placed at the extreme 
anterior point and often projecting in advance of the rest of 
the shell, subinflated or inflated, solid; beaks high and full, 
turned forward over a wide, deep lunule that passes forward 
under them; anterior end truncated squarely or with a slope 
below and usually having a large, faint second lunule; base 
line nearly or quite straight; outline of dorsal slope lightly 
curved; posterior ridge, low, rounded, ending in a rounded 
point at the base of the shell; median ridge very high, rounded, 
curved, usually separated from the posterior ridge by a radial, 
concave depression; surface with irregular growth lines; epi- 
dermis brown to blackish, brownish-green and rayed in young 
shells, scarcely subshining; pseudocardinals radial, often ob- 
lique, torn; lateral of right valve more or less double; muscle 
scars small, deep; beak cavities deep, compressed ; nacre rose- 
colored or white, rarely yellowish or salmon, thinner and 
iridescent behind. 
Length along base 75, from beaks to post-base 84, height 63, 
diam. 41 mm. 
Length over all 110; height 60, diam. 47 mm. 
Length on base 105, over all 115, height go, diam. 58 mm. 
