50 PECTINID^E. 



frame of a fan. Scallops are especial favourites of shell- 

 collectors and amateurs, on account of their elegant 

 shape and their brilliant and varied hues. The curious 

 organs called ' ' ocelli " or eyelets are supposed by some 

 physiologists to be rather highly organized, and even 

 superior to the so-called eyes of most Gasteropodous 

 Mollusca. More than one hundred of them have been 

 counted in a single individual of some species ofPecten. 

 For this reason Poli called the animal Argus. These 

 little eyes have a prismatic lustre, and gleam like pre- 

 cious stones which are set round the inside of a casket 

 lined with mother-of-pearl. Their structure has been 

 lately and independently investigated by Grube, Krohn, 

 and Will. Very young shells of all the species are 

 destitute of ribs ; and they are nearly rhomboidal, owing 

 to their breadth and the size of their ears being propor- 

 tionally greater at that stage of growth than afterwards 

 is the case. In consequence of the Scallops being gene- 

 rally attached or sedentary, the upper valve is more 

 deeply and brightly coloured than the lower one. 



Although all the essential characters of the present 

 genus are uniform and do not vary much in the several 

 species, it has been divided by authors into no less 

 than twenty-eight, most of which will be found enu- 

 merated in the useful Index of Herrmannsen. In nearly 

 all the British species the upper or left valve is the 

 larger, and is also distinguished from the other by its 

 brighter or deeper hue. In Pecten maximus, however, 

 and occasionally in P. septemradiatzis, the lower or right 

 valve is the larger, and almost or quite colourless. The 

 intensity of colour is supposed to depend on the action 

 of solar light, although it is not wanting in animals 

 living in the abysses of the ocean, which the most atte- 

 nuated sunbeam has never directly penetrated. 



