10 



would expect, a good platform for such sessile auimals as 

 Balanus, Zoophytes, Serpula, &c. : and the upper valve, 

 of nearly all the specimens of P. opercularis taken off the 

 Isle 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 shells. 



The majority of Lamellibranchs are equivalve and 

 inequilateral, the right and left valves being mirror 

 images. Pecten, however, shows a departure from this 

 rule as tlie right and left valves are symmetrical, and in 

 some species, e.g., P. maximiis, 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 (PI. I., fig. E, Lg.). The 

 characteristic shape of the valves is given by the auricular 

 area developed on each side of the beak of the shell 

 (PI. I., fig. C, Sh.a.). 



The shell of P. maximns 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 (PI. I., fig. C) being 

 very convex, whilst the left (PL I., fig. D) is quite flat 

 with a concave area near the umbo. In P. ojjercularis 

 the shell is almost equivalve, both valves being convex, 



