RISSOA. 109 



Belfast Bay in 1835" (W. Thompson). It is, probably, 

 an inhabitant of Zostera grounds. 



R. LABiosA, Montagu. 



Large, horn-coloured, sometimes with longitudinal, rib-like 

 folds, sometimes smooth, and with longitudinal tawny lines, no 

 spiral sculpture, nor impressed dots ; whorls flattened : mouth 

 large, patulous, more or less thickened at the outer lip. 



Plate LXXVI. fig. 5 ; Plate LXXVII. f. 1, 2, 3 ; Plate LXXXI. f. 3. 



Turbo membranaceus, Adams, Trans. Linn.Soc.vol.v. p.2, pi. I,f.l4, 15 (badly). 



„ costatiis, PuLTENEY, Hutcliins, Hist. Dorset, p. 45, in part. 

 Helij; labiosa, Mont. Test. Brit. vol. ii. p. 400, pi. 13, f. 7. 

 Turbo labiosus, Maton and Rack. Trans. Linn. Soc. vol. viii. p. 164. — Rack. 

 Dorset Catalog, p. 49, pi. 18, f. 16. — Turt. Conch. Diction, 

 p. 203. — DiLLW. Recent Shells, vol. i. p. 840. — Woon, 

 Index Testae, pi. 31, f. 57. 

 Cingula labiosa, Fleming, Brit. Anim. p. 307. — Brit. Marine Conch, p. 179, 



f. 42. 

 Rissoa „ Brown, Illust. Conch. G. B, p. 10, pi. 8, f. 19. 

 ? „ pulla. Brown, Illust. Conch. G. B. p. 13, pi. 8, f. 25. 



„ membranacea, Loven, Index Moll. Scandin. p. 24 (probably). 



Like most members of its genus, this large species of 

 Rissoa exhibits a considerable latitude of variation in both 

 form and sculpture ; the style of colouring, at least in 

 native examples, is apparently more constant, the Hneated 

 painting being confined to the thinner and smoother indi- 

 viduals. In the more characteristic specimens, the shape 

 ranges from oval-conic to oblong-conic, the texture is 

 rather solid, yet a little transparent, resinously lustrous, 

 and of an uniform pale horn-colour or dirty white. The 

 earlier turns are quite smooth, the body and two preceding 

 whorls are decorated with longitudinal pliciform ribs, that 

 range in prominence from strong and projecting to de- 

 pressed and almost obsolete ; they usually widen below, 



