l66 PECTEN. 



This species sometimes grows to the size of a large 

 oyster, but some specimens are only three inches long. 

 It is rarely cast up alive by storms, but dead shells 

 are not uncommon. It is most abundant in northern 

 waters. 



Unlike the last species, the Pectens or Scallops 

 remain free during their whole life, though they some- 

 times spin a byssus, or cable of threads, and attach 



Fig. 139. 



themselves to pieces of sea-weed. They swim by 

 opening and shutting the valves of the shell, and they 

 have small eyes along the edge of the mantle. The 

 valves are connected, as in quite a group of similar 

 species, by a single, large, central muscle, instead of 

 by two, as in most of the bivalves. 



The first species, Pecten czquisulcatus, Cpr., Pek'- 

 ten e-qui-sul-ka'-tus, is a southern shell, and its beau- 

 tiful form and markings are shown in Fig. 159. 



