422 PATELLID^. 



features for description, but those few are likewise sus- 

 ceptible of great modifications. The P. vulgata is not the 

 least variable of its genus, and exhibits considerable varia- 

 tion in shape and colouring ; which seems partly to depend 

 upon growth, partly to result from local circumstances. 

 Middle-aged specimens — generally the most characteristic 

 stage in Patella, — of nearly an inch and a half long, 

 are of a subovate figure, subcorneal, strong, and for the 

 most part of a rather pale olive or dirty and somewhat 

 olivaceous yellow cast ; in the former case, obscurely 

 marked with rather narrow rays of dark grey ; in the 

 latter, with the rays generally much interrupted, chiefly 

 conspicuous in the more depressed portion of the surface, 

 and often of a rich chocolate brown. In one of our 

 varieties the darker rays are very obscure, and the small 

 ribs are somewhat radiatingly speckled with white ; in 

 another the entire exterior, as well as the inner edge, is 

 of a dark brown, and the interior, the spatula excepted, 

 is of a very pale olive hue. The inside partakes of the 

 external painting (the substance of the shell, and not 

 merely the superficies, being coloured) but is somewhat 

 paler, and is always slightly iridescent ; the spatula- 

 shaped central portion is of an uniform opaque and rather 

 bluish white, and not edged with orange. The margin is 

 less ragged than in the succeeding species, but is angularly 

 undulated in the more strongly ribbed forms, almost plain 

 (but never quite so, unless abraded) in the simply striated 

 ones. These are the two principal varieties as to sculp- 

 ture : in the more characteristic individuals of the former, 

 and such are generally conical, there are about twenty- 

 five strong and bluntly angulated unarmed ribs, each with 

 about three or four interstitial stria' ; in the latter the ribs 

 are almost obsolete, or actually divided into irregular 



