QUADRULA 867 
The base and dorsal outlines are usually so curved that the 
shell is almost evenly short elliptical. It is less inflated, less 
solid and more evenly elliptical than Q. beadleiana. 
QUADRULA SUCCISSA (Lea). 
Shell subrhomboid, convex or subinflated, somewhat inequi- 
lateral, subsolid or solid; beaks apparently only moderately full 
and high; anterior end, obliquely truncate above, rounded be- 
low; base line straight or nearly so; outline of posterior end 
curved from the beaks to the base; posterior ridge well devel- 
oped, subangular above, inclined to be double below ; surface 
finely and unevenly, concentrically striate; epidermis reddish- 
brown, sometimes showing faint, dark rest marks, scarcely 
shining; pseudocardinals triangular, split up or striated; lat- 
erals curved, scarcely double in the right valve; beak cavities 
rather deep, compressed; muscle scars impressed; nacre pur- 
plish or violet. 
Length 44, height 31, diam. 18 mm. 
Type locality, West Florida. Also, southern Alabama. 
Unio succissus Lea, Tr. Am. Phil. Soc.; X, ‘1852, p. 275; pl. 
xxJ, fig. 32; Obs., V, 1852, p. 31, pl. xx1, fig. 32—SOweErRBy, 
Conch. Icon., XVI, 1866, pl. xxx, fig. 174.—SIMPSON, 
Pie ley SoiNateiMitis., SVs 1802, p. 209, pl. Lxxi,; fig. 5. 
Maregaron (Unio) succissus L&A, Syn., 1852, p. 24; 1870, p. 38. 
Ouadruia succissa SIMPSON, Syn., 1900, p. 785. 
Unie cacao Wes, Pr Ac. N. Sct. Phila., TIT, 1850; p. 154.5 Jil. 
AG Ne sci euild., 1V, 1860, p. 344, pl. ivi, fig. 160: :Obs., 
WILE 18005 9: 26; pl. Evi, figs 160. 
Margaron (Unio) cacao Lea, Syn., 1870, p. 54. 
The type of this is from West Florida and is a subsolid, 
scarcely inflated, reddish-brown shell with a purple nacre. It 
is an older shell than Lea’s cacao, but I believe that the two 
are absolutely identical. In Lea’s collection there is a shell 
which he calls Unio succissus, from New Orleans, that I be- 
lieve is chickasawhensis and another bearing that name from 
Alexandria, Louisiana, is, I think, Quadrula cerina Conrad. 
