938 QUADRULA 
ridge scarcely developed above, sometimes feebly and widely 
double below and ending in a wide, ill-defined biangulation ; 
surface throughout in front of the posterior ridge densely 
covered with pustules, looking as if engine-chased, rarely in 
somewhat chevron-shaped patterns; behind the front part of 
the posterior ridge is a series of fine, curved, subradial ridges ; 
epidermis wrinkled, scarcely shining, various shades of brown. 
or brown and green; pseudocardinals small, radially striate; 
laterals rather delicate, curved; beak cavities moderately deep, 
compressed; muscle scars not deep; nacre lurid brownish, 
thinner behind where the pattern of sculpture shows through.. 
Length 58, height 45, diam. 20 mm. 
Borneo. 
Unio radulosus Drourt and CHAprgEr, Mem. Soc. Zool. Fr., V, 
18Q2, p.. E50, pl. Vv, hes.,00-12: 
OQuadrula radulcsa StMPSON, Syn., 1900, p.°803. 
Discomya radulosa Haas, Con. Cab. Unio, 1910, pl. xvi, figs. 
T-2. 
A decidedly interesting and unique shell. In many cases the 
sculpture in front of the posterior ridge is almost as perfect 
and regular as though it had been turned out by machinery. 
The lenticular form the curiously varigated epidermis, the 
visibility of the sculpture through the posterior nacre are 
striking characters. Although I cannot be certain as to the 
systematic position of this form, yet I believe that it is rather 
closely related to the heavy Chinese forms that I have placed 
in Quadrula and probably most near to the group of Q. leat. 
Var. rhomboidea Simpson. 
Shell longer than the type, rhomboid, the posterior ridge 
widely double, ending at and near the base in a wide biangula- 
tion ; base line incurved behind ; nacre lurid, dark purplish lead- 
color. 
Length 57, height 37, diam. 22 min. 
Selrocany, Borneo. 
Ouadrula radulosa var. rhomboidea SIMPSON, Syn., 1900, p- 
803. 
