214 testaceous mollusca. 



Division C. 



A linear tooth tinder the dorsal edge. 



U. BiALATA. Desh. in Lam. — Dipsas Plicatus. Leach.— 

 Mytilus DuBius. Gmel. — Anodon Dipsas. BIain.t.66.f.3. 

 — A. Alatus. Sow — Symphonota B. Lea. on U. 1. 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) . . 3|. — Canton. 



U. DiscoiDEus. Lea. — Symphonota D. Lea. Trans. Am. 

 Ph. 5. t. 11./. 33.— U. Tenuis .j- Anod. T. Grif. Cuv. 

 Transverse, subrhomboidal, dorsal edge nearly straight, ventral 

 strongly arcuated ; veiy thin, compressed, inequilateral, finely 

 ■wrinkled, connate anteriorly : beaks very slightly undulated, com- 

 pressed, ligament linear ; cuticle dark bi'own, nacre white and 

 irridescent ; teeth in both valves forming a simple line. 2f . . 3-^^ — 

 Java? 



HYRIA. 



Equivahe, 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. /. l.—D. p. 54.— TF. t. 2./. 36.— List. t. 160. 

 y. 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. AvicuLARTs. Lam. \. — Del. t. 12. f. 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. 3^. — Guiana. 



