6# Gray on Helkina. 



Testa subulata ovata, fusca. 



Balea tristensis. Leach Mss. 



Tristan d' A'Cunha. Capt. Carmichael. Mus. Brit. Nostr. 



Shell, subulato-ovate reddish brown, axis ^^, diameter ^ of 

 an inch. 



3. Balea ventricosa. ^^ • '^^ f • '^ • 



Tesla lanceolato-ovata, pallide fusca. 



Balea ventricosa. Leach Mss. Brit. Mus. 



Tristan d' A'Cuuha. Capt. Carmichael. Mus. Brit. Nostr. 



Shell, lanceolato-ovate, pale brown, axis J^, diameter ^ of 

 an inch. 



Art. X. Monograph of the Genus HeUcina^ hy Mr. 

 John Edward Gray. 



Helicina. Lamarck Sys. but not of De Montfori. ' / 



Olygyra. Say. Amer. Conch. 



Char. dif. Animal uuisexuale, capite et disco distinctis, ten- 

 taculis duobus contractilibus, oculis subsessilibus^ cavitate pul- 

 monali aperta. Pallii marginibus incrassatis. 



Operculo annulato corneo. 



Testa spiralis, apertura semi-orbiculata. Peristomate reflexo 

 columella basi callosa. 



Animal head distinct, beak short, apex two lipped. Tentacula 

 two, filiform, contractile, eyes two, nearly sessile, at the outer 

 base of the tentacula. 



Respiratory cavity open, lined by the reticulated pulmonary 

 vessels. 



Body spiral. Mantle, edge thickened, free, ventral disk, or 

 sucker tongue-shaped, adductor muscle attached to the columella. 



Organs of reproduction distinct, the sexes on separate in- 

 dividuals. 



Operculum annular, horny or very thin shelly ; nucleus nearly 

 central, placed rather towards the innerside. 



