272 ostreadjE. 



Thompson). It is found on the coast of the Continent, 

 from Norway to the Mediterranean. It is found fossil in 

 the Crag. 



PECTEN. Brugiere. 



Shell oblong or suborbicular, regular, inequivalve, sub- 

 equilateral, closed, eared at each side of the hinge ; surface 

 smooth or sulcated with radiating, often scaly, ribs, or 

 minutely striated and granulated in various directions. 

 Beaks approximated. Hinge line straight, with a mar- 

 ginal linear ligament, and a central cartilage lodged in a 

 triangular pit under the beak of each valve ; one valve 

 with a byssal sinus. Interior with an entire pallia! im- 

 pression, and a single large subcentral muscular scar. 



Animal shaped as the shell, mantle freely open, with 

 pendant margins bearing (usually two) fringes of tentacu- 

 lar filaments, the one series at their fixed, the other at 

 their free border. Among the former are ranged globular 

 shining ocelli. No siphonal tubes. Body large, apiculated. 

 Sexes united."" Foot small, cylindrical, with a byssal 

 groove, from whence a weak byssus is spun, mostly when 

 the animal is young. Mouth surrounded by foliaceous 

 leaflets and two pair of labial tentacles which are smooth 

 externally, pectinated internally. Branchial leaflets equal, 

 each pair partially doubled on itself. 



This beautiful genus, which includes more than one hun- 

 dred existing species and a very great number of fossils, 

 has several very elegant and useful representatives in the 

 British seas. The majority of Pectens are tropical, and 

 among them we find the most brilliantly painted of bi- 

 valves. They live either solitary or in great assemblages, 



* See Milne Edwards in Ann. des Sc. Nat. xviii. p. 321. 



