214 TESTACEOUS MOLLUSCA. 



Division C. 

 A linear tooth under the dorsal edge. 



V. Bialata. Desh. in Lam. — Dipsas Plicatus. Leach. — 

 Mytilus Dubius. Gmel. — Anodon Dipsas. Blain.t. 66./. 3. 

 — A. Alatus. Sow — Symphonota B. Lea. on U. I. p. 59. 1. 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) . . 3f , — Canton. 



U. Discoideus. Lea, — Symphonota D. Lea. Trans. Am. 

 Ph. 5. t. 11. /. 33.— U. Tenuis ^ Anod. 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. 2J- . . 3 T 9 ff - — 

 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. Syrmatophora. Sow. G. f. 1. — Reeve, t. 90. f. 1.— Mya 

 S. Gronov. t. 18./. 1.— D. p. 54.— W. t. 2.f.36.—List. t. 160. 

 f. 16. — H. Avicularis. 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. 2\ . . Guinea ? 



H Avicularis. Lam. 1. — Del. t. 12./. 9. — H. Elongata. 

 Swain. Ex. 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. 3J-. — Guiana. 



