54 BIVALVE SHELLS. 



Cytherea incerta, Sow. Thes. Conch. p. 61/. pl. 128. f. 17- 

 Hab, S. Joan. Coll. Cuming. 



IV. Species duhice. 



29. Trigona nucula. 



T. testa cordato-ovata, transversira striata, striis antice argutis, 

 medio obsoletis, alba ; extremitate utraque acutiuscula ; mar- 

 gine dorsali antico rectilineo, postico arcuato, anticum bis 

 sequante ; lunula cordata, parum distincta ; area nulla ; liga- 

 mento extiis vix conspicuo ; dentibus in valva dextra quatuor, 

 geminatis, prseter anticum internum ad foveam, in valva sinis- 

 tra tribus, antico remoto ; sinu palliari acutangulo, mediam 

 testam haud attingente. 



Trigona nucula, Philippi, Zeits.fiir Malac. 1848, p. 144. no. 89. 

 Rab. In mari Chihensi vel Peruviano. 



30. Trigona dubia, Sow.jun. See "T. damaoides," p. 47. 

 Hab. China. 



Genus 6. DIONE. 



Auinial ovato-oblongum, posterius tracheis duabus coadu- 

 natis terminatum, aperturge trachearum ad marginem tentaculatse, 

 tentaculis simphcibus; pallii margines antice inferneque dis- 

 junctae, lobse plicatae, posteriiis supra trachearum basin tentacu- 

 latffi ; pes maximus, compressus, linguiformis ; labiarum appen- 

 dices trigonse, angustae, acuminatse; branchise elongata^, inaequales, 

 transversse, posterius connectse, acuminatge, exteriores angusti- 

 ores. 



Testa ovata, transversa, inacquilateralis, clausa ; marginibus in- 

 tegris saepius obtusis ; cardine in utraque valva tridentato, dente 

 laterali antico, lunulari adjuncto ; impressio pallii postice sinu- 

 osa ; sinus profundus, latus, semiovatus. 



Vulvaria, Klein (1744), Ostrac. p. 155. 



Venus (spec.), Linn. (1758) Syst. Nat. ed. 10. p. 684; (1/64), 



Mus. Ulric. p. 497; Syst. Nat. ed. 12. p. 1128. 



Chemnit2,Schrdter,Miirray,Born, Barbut, Gmelin, Billwyn, 

 Wood. 

 Pectunculus, Ba Costa (1778), Conch. Brit. p. 184. 

 Cahsta, Calistoderma, Poli (1795), Test. Sicil. ii. 252. 

 Meretrix (ex parte), Lamk. (1799) Mem. de la Soc. d'Hist. Nat. 



de Paris, p. 85 ; (1801), Syst. des An. s. Vert. p. 122. 

 Cytherea (ex parte), Lamk., Roissy (1805), Moll. Buf. vi. 336; 



