QUADRULA 877 
rayed, cloth-like; pseudocardinals ragged, the anterior one in 
the left valve compressed and joined to the posterior one; 
laterals curved, that of the right valve partly double; muscle 
scars impressed, the posterior ones round; nacre bluish-white, 
thinner behind; beak cavities deep, compressed. 
Length 57, height 48, diam. 33 mm. 
Mississippi; west to central Texas north to Arkansas. 
Type locality, Dallas, Texas. 
Unio chunu, Es, Pr. At. N, Sci; Phila.; V, 186%, p. 392; Jl. 
Hensel i tila, Vo Ta62..p. 160, pl. XxvIL, p. 265; Obs., 
DXrs69.sp. 18; ple xxvun, fig, 265. 
Margaron (Unio) chunu Tea, Syn., 1870, p. 38. 
Quadrulo chunu Simpson, Syn., 1900, p. 787. 
Close to wndata and certain specimens can scarcely be sepa- 
rated from that species. It is generally less triangular, the 
beaks are not so full and high, the posterior ridge is not so 
pronounced and it has a smoother, less rude shell than that 
species. 
Var. nasuta n. v. 
More elongated, more drawn to a point at the posterior base 
than the type, less solid, with a higher posterior ridge. 
Length 55, height 39, diam. 30 mm. 
I formerly thought this was a variety of cerina but since 
seeing what I believe are valid specimens of that I am inclined 
to make it a variety of chuni?. ‘Typically it is quite different, 
but material before me seems to connect the two. 
QUADRULA CASTANEA 0. S. 
Shell irregularly ovate, inflated, solid, inequilateral; beaks 
full and elevated ; posterior ridge fairly well developed, single 
or imperfectly double, narrowly rounded, angular or slightly 
biangulate ; anterior end rounded or subtruncate above, some- 
times having an angle at the front end of the compressed 
lunule; base line lightly curved to straight; outline of dorsal 
slope lightly curved from the beaks to near the base, sometimes 
raised into a low angle behind the ligament; surface rather 
