124 LITTORINID^. 



its inner margin : the parietal enamel is usually profuse 

 in adult examples. A sixth of an inch for the length, 

 and a line or rather more than a line for the breadth, 

 are the ordinary proportions. 



The variety termed grapMca by Turton, is rather 

 stronger than usual, and has its zones much more faintly 

 displayed. It is not uncommon at Weymouth, under 

 stones near the old castle, &c., (S. H.). 



In typical specimens of the aberrant form rupestris, the 

 shell is nearly of an uniform white, and the spiral striae 

 are obsolete above the angulated commencement of the 

 basal slope. The seeming subsutural line is not impressed, 

 but is merely the overlapped base of the preceding turn 

 revealed by the more than ordinary transparency of the 

 shell. 



The animal is of a yellowish white, sometimes (in the 

 normal form) slightly tawny, sometimes (in var. ru- 

 pestfis) more of a milky hue. The snout is prominent, 

 narrow, and translucent, showing the jaws and tongue 

 shining through ; the tentacles are very long and linear, 

 bearing the conspicuous black eyes on their opaque white 

 bulging bases. The foot is narrow and oblong, angled, 

 but not sharply, in front, obtusely pointed behind. The 

 caudal cirrhus, if present, is small ; we have not been able 

 to see it. When the creature is at rest the foot is much 

 contracted, and the tentacles are turned back on the shell. 

 When in motion it moves its tentacles in a waving manner 

 alternately ; a habit common to other species of the genus. 



Rissoa cingillus is strictly a littoral animal, abounding 

 between tide-marks in muddy, rocky, and stony places 

 almost everywhere around the shores of Britain and 

 Ireland. The variety grapMcus is scarce ; it occurs at 

 Langland, near Swansea (Jeffreys). The form rupestris 



