214 TESTACEOUS MOLLUSCA. 
Division C. 
A linear tooth under the dorsal edge. 
U. Brauata. Desh. in Lam.—Drirsas Puicatus. Leach.— 
Myrixtus Dusius. G'mel.—Anovon Dipsas. Blain. t. 66. f. 3. 
—A. Atatus. Sow —Symrnonora B. Lea. on U. 1. p. 59. t. 14. 
Triangular-ovate, inequilateral, subventricose, transversely and finely 
wrinkled, dorsal edge suddenly raised at its extremities into two 
wings, the anterior one the largest : valves thin, connate before and 
behind the beaks which are not prominent but undulated as well as 
the base and summit of the anterior wing : sides and ventral edge 
simply rounded : cuticles having yellow and purple brown with 
green oblique rays, nacre pearly and irridescent: one lamelliform 
curved tooth in each valve. 2 (from beak). .32.— Canton. 
U. Discotipeus. Lea.—Sympnonota D. Lea. Trans. Am. 
Ph. 5. t. 11. f. 33.—U. Tenuts §& Anop. T.. Grif. Cuv. 
Transverse, subrhomboidal, dorsal edge nearly straight, ventral 
strongly arcuated; very thin, compressed, inequilateral, finely 
wrinkled, connate anteriorly : beaks very slightly undulated, com- 
pressed, ligament linear; cuticle dark brown, nacre white and 
irridescent ; teeth in both valves forming a simple line. 22. .3,9,.— 
Java? 
HYRIA. 
Equivalve, obliquely triangular, auriculated, the dorsal edge trun- 
cated and straight: hinge with two little elevated teeth, the 
posterior or cardinal one divided into numerous diverging por- 
tions, (the inner portions being the smaller); the anterior or 
lateral tooth very elongated and lamellar. Ligament external 
and linear. 
H. Syrmaropuora. Sow. G. f. 1.—Reeve. t. 90. f. 1.—Mya 
S. Gronov. t. 18. f. 1.—D. p. 54.—W. t. 2. f. 36.— List. t. 160. 
f. 16.—H. Avicunaris. Var. B. Lam. Ovate-subrhomboidal, 
dark olive, nearly smooth, hinge margin straight and forming short 
wings at its extremities, anterior edge almost direct and straight so 
as nearly to form a rectangle with the ventral : posterior side nar- 
row, the edge uniting with the ventral in an oblique curve : tumid, 
the anterior slope very flattened and bounded posteriorly by an obtuse 
ridge. 23.. Guinea? 
H. Avicutarts. Lam. 1.—Del. t. 12. f. 9.—H. Etoneata. 
Swain. Ha. Con. t. 24. Oblong-subtriangular, hinge margin with 
produced and narrow wings at its extremities : anterior edge form- 
ing an acute angle with the ventral edge, which forms one uninter- 
rupted line with that of the very attenuated posterior extremity : 
convex, nearly smooth, the cuticle brown and the anterior slope 
simple. 33.—Guiana. 
