The Pectens (Scallops). 



By W. T. Manger. Read November \ofh, 1904-. 



Order — Lamellibranchiata ( Plate gilled Molluscs). 



/??/«//>■— PECTENID.*:. 



I SUPPOSE there is no member of the great class Mollusca that is 

 better known to the majority of us than the Pectens (scallops). 

 Most of us have eaten them, and all of us have seen them exposed 

 for sale in the fishmongers' shops. I don't know that I can add 

 anything new to the numerous descriptions of this animal that have 

 appeared (notably that able work of our President, entitled " Shell 

 Life"), but I thought that a few foreign specimens for comparison 

 with our English forms would be both interesting and instructive. 

 In their scientific order they follow on closely to the oysters, but 

 they differ from them very much, both in thdr internal economy 

 and in their form, colour, and sculpture. The British Pectens, of 

 which there are ten or eleven species, vary very much in colour and 

 appearance, and also in size. The species commonly eaten is 

 Pecten maximus, but P. opercidaris is also eatable. P. tnaximus is 

 the largest British Pecten, and may be taken as the type of the 

 family. It is not within the scope of these notes to give you a 

 scientific description of the animal that makes this shell ; it is suffi- 

 cient to remind you that the two valves are held together by the 

 adductor muscle, and joined with a strong ligament. The action of 

 this india-rubber-like ligament is in opposition to that of the adductor 

 muscle, so th.it when the latter close the valves they compress the 

 ligament. The ocelli are placed along the two edges of the mantle 

 so as to receive the light when the shell gapes ; these eyes are 

 remarkably large and prominent and vary in number very much. 

 In P. maximus, P. opercuhiris, and P. jacobcviis there are 80 to 120. 

 They are highly developed, and bear a considerable resemblance to 

 the vertebrate type of eye, but for all that their range of vision does 

 not appear to be very great. The Pecten has ceased to use its foot 

 as an organ of progression, but they can flit or fly (especially when 

 young) for considerable distances in the water by flapping the valves 

 together ; as they grow older they become more sedentary, and are 

 often found thickly covered with acorn-shells, Serpula, Zoophytes, 

 etc. They get their living in the shape of minute particles, animal 

 and vegetable, which are contained in the water which they breathe. 

 Most of the Pectens spin a byssus when young, by which they can 

 attach themselves to rocks, etc. There are about 180 species of 

 Pectens known, and over 400 are recorded as fossil from the 



