EISSOA. 353 



LITTORINA VINCTA, Montagu. 



L. vincta, Brit. Moll. iii. p. 62, pi. 72. f. 10, 11, 12; pi. 74. f. 7, 8 ; 

 pi. 86. f. 6, 7, 8; (animal) pi. G.G. f.4. 



LITTORINA CRASSIOR, Montagu et nobis. 

 Lacuna crassior, Brit. Moll. iii. p. 67, pi. 72. f. 5, 6. 



RISSOA, Freminville. 

 R. ULV^E, Pennant. 



R. ulna, Brit. Moll. iii. p. 141, pi. 81. f. 4, 5, 8, 9; pi. 87. f . 2, 8 ; 



(animal) pi. J. J. f. 8. 

 R. subumbilicata ?, Montagu. 



, Brit. MoU. iii. p. 137- 



Animal spiral, of 6-8 volutions ; mantle plain ; head a long 

 dark proboscidiform muzzle, emarginate in the centre in front, 

 marked with two transverse bars, and its margins edged with 

 the same dark colour ; buccal disk pale brown or yellow, with 

 a vertical fissure, from which, when the animal gapes, a pair of 

 curved jaws are seen; these are the anteal termination of the 

 lingual riband, which makes its way to the stomach through a 

 pair of fleshy, or rather horny, plates, the whole forming what 

 is called the masticatory apparatus ; tentacula very long, cylin- 

 drical, slender, pointed, very little setose, whitish-yellow, with 

 a black bar at a short distance from their termini ; eyes at the 

 external bases on short protuberances; foot short, truncate 

 and auricled in front, rounded, and, in some individuals, 

 slightly emarginate posteriorly. In the lighter coloured 

 variety, the upper part is a pale brown, beneath yellowish- 

 white, with a border of minute pale golden flakes, with some- 

 times a dark bar running through the centre of its posterior 

 part; in the darker variety, the upper part of the foot is 

 clouded with very fine dark lead-colour to its paler hues, 

 underneath pale brown. 



These animals creep with great rapidity, and float with the 

 foot uppermost by means of an hydrostatic apparatus, as air- 

 bubbles are seen continually to proceed from the aperture ; 

 they are strictly littoral, and inhabit in myriads the green 

 oozes of the estuaries. 



2A 



