BIVALVE SHELLS. 241 



obtuso circumscripto ; cardine lato, crasso, brevi, inaequaliter 

 tridentato, dentibus angustis, elongatis, pavallelis, apice vix 

 canaliculatis ; dente lateral! antico maximo, crasso, cardine 

 valde approximato, postico longiore, aiigusto, valde separate. 



Cyrena cyprinoides, Gray, Ann. Phil. 1825, p. 137. 



Velorita cvprinoides, Gray in Griff. Anim. Kingd. pi. 31. f. 5 ; 



Ann. ^'Mag. N. H. ser. 2. xi. 39. 

 Venus cyprinoides. Gray in Wood, Ind. Test. Suppl. pi. 2. f. 11. 



Hub. Fluviis Japonieis. 



Genus 4. CYRENA. 



Animal ovatum, transversum; pallium ad margines simplex 

 vel fimbriatim, postice tracheis binis basi connatis, brevibus, ter- 

 minatum. Pes magnus, compressus, ovato-trigonus ; labiarum 

 appendices elongatse, ovatae, ti'igon8e,necnon conjunctse ; branchiae 

 insequalissimae, interna major subquadi-angularis, externa minima 

 subtrigona. 



Testa ovata vel subtrigona, crassa, solida, epidermide vestita, 

 cardo in utraque valva tridentatus, dentes paulo divergentes ; 

 dentes laterales duo, inaequales ; antico breviore cardine approxi- 

 mato ; impressio pallii simplex. 



Venus, Chemn. (1/82) Conch, vi. 333. 



Cyclas (ex parte), Brug. (1792) Ency. Meth. pi. 301, 302. 



Lamk. (1802) Syst. des An. s. Vert. 

 CjTcna (pro parte), Lamk. (1818) An. s. Vert. v. 551. 

 Cyrena iS, Gray (1847), Proc. Zool. Sac. p. 184. 

 Geloina, Gray (1840), Syn. Mus. Brit. 1844, p. 75. 

 CjTena, Gray (1851), Ann. <^ Mag. Nat. Hist. ser. 2. xi. 48. 

 Polymeroda, Rajin. Ann. Gen. ScL Nat. Brux. 1820, v. 219. 



Synopsis Specierum. 

 I. Cyrena vera, 



A. Testa ovata, suborbicularis vel subtrigona, epidermide lamel- 



losa vel squamulosa. 



a. Testa subtrigona, 1-13. 



b. Testa ovata, 14-30. 



e. Testa suborbicularis, 31-34. 



B. Testa trigona, tumida, subcordiformi, epidermide nitente. 



35-41. 



11 



