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 branchiz 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. maximus has the upper 
valve flat, with a concave area at the beak. 
P. maximus, Linnzeus. 
P. maximus, Brit. Moll. ii. p. 296, pl. 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 poimt, with a pale red-brown line, the 
under surfaces being white; the cirrhi of the convex valve 
E 2 
4 
