QUADRULA 937 
This is a robust, solid, quite inflated form, which has some 
of the characters of the nodulosa group. The form however is 
much like that of QO. cornuum-lune. 
QUADRULA DIVERGENS (Benson). 
Unio divergens Benson, Jl. As. Soc. Beng., XXIX, 1855, p. 
ig. 
Quadrula divergens SIMPSON, Syn., 1900, p. 802. 
Unio divergens Benson, from Chusan Island, China, has 
never been figured, so far as I know. It probably groups 
here and may be a form of Q. leai. The description is not now 
accessible to me. 
Subgenus Discomya Simpson, 1900. 
Discomya SIMPSON, Syn., 1900, p. 802. 
Shell subsolid, round obovate or subrhomboid, lenticular, 
rather compressed, widely, faintly biangulate behind, with 
scarcely any vestige of a posterior ridge; beaks very low, 
sculpture not seen; front half of the shell densely covered with 
fine pustules arranged in curved rows in two directions as if 
engine-chased, over which the epidermis is wrinkled. The 
hinder half is covered with fine, radiating and undulating 
corrugations, curved upward posteriorly, which are slightly 
nodulous and show through on the inside of the shell; one 
slightly compressed pseudocardinal in the right valve and two 
in the left; one delicate, curved lateral in the right valve and 
two in the left; beak cavities deep, compressed; nacre lurid; 
pallial line showing a slight posterior sinus. 
Type, Unio radulosus Drouet and Chaper. 
QUADRUILA RADULOSA (Drouet and Chaper). 
Shell obovate with a tendency towards being subrhomboid, 
convex, subsolid, inequilateral, lenticular; beaks apparently 
not full or elevated; anterior end rounded or sometimes. a little 
truncate and angled above; base line lightly curved ; dorsal line 
behind the beaks elevated almost into a wing, the hinder part 
of the wing and dorsal slope obliquely truncated; posterior 
