PECTEN. 51 



colours. The mantle is pale yellow, furnished, as is usual in 

 the Pectens, with a fixed and free margin ; the latter is clothed 

 with about twenty long, white, triangular, frosted cirrhi with 

 shorter intermediates ; from the minuteness and delicacy of the 

 animal the filaments of the fixed margin were not detected ; 

 the free margin between the cirrhi is marked with blotches of 

 all sizes, of the colours yellow, bistre, rufous, and black ; the 

 ocelli are 16-20 ashy circles, having in their centre a minute 

 ring or pupil of a smoke colour. The branchiae vary from 

 light yellow to dark lead colour, but the very fine darker lines 

 are generally relieved by intermediate lighter ones ; they, like 

 their congeners, have the lower part of the area of each gill- 

 plate reflexed on the upper, forming subcircular pouches. The 

 small foot, producing a byssus, is situate very high, almost 

 immediately under the anterior dorsal margin, and varies from 

 white to vermilion. These variations in colour of the shell 

 and organs of the same species are one of the characteristics 

 of the tribe. The foot appears to have little power of loco- 

 motion, but by spinning a byssus it produces a mooring appa- 

 ratus. The animal, by flapping the valves, effects a rapid 

 progression. 



This very distinct species has been considered by some as 

 the young of Pecten maximus, but the convexity of both valves 

 negatives this idea. At all ages the P. maximum has the upper 

 valve flat, with a concave area at the beak. 



P. MAXIMUS, Linnaeus. 

 P. maximus, Brit. Moll. ii. p. 296, pi. 49. 



In this beautiful and well-marked species, both by the shell 

 and the animal, the inner margin of the mantle has only a 

 simple row of very short, white cirrhi; the fixed anterior 

 margin has three ranks of filaments of different lengths not 

 deposited in perfect serial order, the largest and longest are 

 pointed, and on retraction become curled in a spiral form; 

 all the cirrhi on the upper or flat valve are marked in the 

 centre, from base to point, with a pale red-brown line, the 

 under surfaces being white; the cirrhi of the convex valve 



E2 



