306 OSTREADJE. 



A Mediterranean shell ; introduced by Pennant as " a rare 

 shell in Great Britain," and said by Pulteney to have been found 

 on the Dorset coast. As no specimens have been obtained of late, 

 although never was the dredge so actively employed as during the 

 last few years, it is to be presumed that this shell was included as 

 British from that spirit of easy credulity which tempted our older 

 writers to admit as indigenous so many exotic shells into their 

 tvorks, on the careless authority of their friends' mixed collections, 

 <nnl imperfect memories. 



OSTREA. Linn-eus. 



Shell variously shaped, inequivalve, more or less in- 

 equilateral, often thick and irregular, upper valve most 

 frequently flat or concave, under one convex, surface 

 foliated, or with radiating furrows ; hinge without teeth ; 

 ligament lodged in a pit in each valve, the beak behind 

 that of the under valve often produced and exhibiting a 

 furrowed ligamental area. Muscular scar subcentral, pal- 

 lia! impression obscure, entire. 



Animal shaped like the shell, its mantle freely open 

 and without tubes, the edges double, and each bordered 

 by short tentacular fringes ; no conspicuous ocelli ; bran- 

 chial leaflets not doubled on themselves ; labial appendages 

 triangular, connected around the mouth by a plain mem- 

 brane ; foot obsolete. 



The sexes of oysters, according to recent observations 

 of Quatrefages, are distinct. Our most valued bivalve 

 belongs to this genus, and is the only species of it now 

 inhabiting our seas. During ancient epochs, as we learn 

 from the fossils of both tertiary and secondary strata, 

 many more kinds of oyster lived within our area, and 

 multiplied so as to rival the contents of any modern 

 oyster-beds. The discoveries of geologists open scenes of 



