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342 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
would expect, a good platform for such sessile animals as 
Balanus, Zoophytes, Serpula, &c.; and the upper valve, 
of nearly all the specimens of P. opereularis taken off the 
Tsle of Man, and numbering several hundreds, was covered 
with a Halichondrioid sponge of a rich red colour. 
THE SHELL. 
Scallop shells are well known at most seaside resorts. 
They are sold as ornaments, and have been put to various 
uses by the fishermen. They were used, moreover, in very 
early times, and it has been supposed that the flat valves 
were the plates and the hollow ones the drinking cups 
of Fingal and his heroes. Until recently, in the Isle of 
Man, primitive lamps were made from the deeper sliells. 
The majority of Lamellibranchs are equivalve and 
inequilateral, the right and left valves beimg mirror 
images. Pecten, however, shows a departure from this 
rule as the right and left valves are symmetrical, and in 
some species, e.g., ?. maaimus, are very unlike each other. 
The equilateral character is in some species disturbed by 
the areas near the hinge line being unequal in size. The 
hinge line is practically straight, and a strong internal 
cartilaginous ligament is situated in a deep triangular 
pit, under the beak of each valve (Pl. I., fig. HE, Zg.). The 
characteristic shape of the valves 1s given by the auricular 
area developed on each side of the beak of the shell 
CPt a ice CaaS tice): 
The shell of P. mazzmus is brittle and rather light 
for the size, which is what one would expect since a 
heavy shell would be detrimental in swimming. It is 
very inequivalve, the right valve (Pl. I., fig. C) being 
very convex, whilst the left (Pl. I., fig. D) 1s quite flat 
with a concave area near the umbo. In P. opercularis 
the shell is almost equivalve, both valves being convex, 
