«? Gray on HeUcina. 



Testa subulata ovata, fusca. 



Balea tristensls. Leach Mss. 



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



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

 an inch. 



3. Balea veniricosa. 



Testa lanceolato-ovata, pallide fusca. 



Balea ventrirosa. Leach Mss. Brit. Mus. 



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



Shell, lanceolato-ovate, pale brown, axis -^, diameter ^^ oj 

 an inch. 



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

 John Edward Gray. 



Helicina. Lamarck Sys. but not of De MontforcL 



Olygyra. Say. Amer. Conch. 



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

 taculis duobus contractilibus, oculis subsessilibus^ cavitate pul- 

 monali aperta. Pallii marginibus incrassatis. 



Opercido annulato corneo. 



Testa spiralis, apertur^ 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, hocny or very thin shelly ; nucleus nearly 

 central, placed rather towards the innerside. 



