OSTEEA. 55 



OSTKEAD.E. 



One genus, with a single proteiform species, constitutes 

 this peculiarly British family. Ostrea is the Lamarckian 

 monomyal type. What has been said on the Anomiadce and 

 Pectinida renders further detailed remarks unnecessary. We 

 will only observe, though the general form of the branchial 

 laminae is similar to those of the Pectines, that they are in 

 their composition very distinct ; the complete absence of the 

 byssal foot is another important deviation, and in other re- 

 spects it is eminently distinguished from Pecten; Ostrea is 

 generally fixed by the under or convex valve, and has, if any, 

 a very limited locomotion, whilst Pecten is almost always free, 

 and can perform the most rapid leaps and movements. 



OSTREA, Linneeus. 

 O. EDULIS, Ibid. 



O. edulis, Brit. Moll. ii. p. 307, pi. 54, (animal) pi. T. f. 1. 

 O. parasitica, Auct. 



Animal orbicular, subcompressed, of a pale drab colour 

 throughout ; mantle thin at the beaks, gradually thickening 

 to the ventral range, entirely open, except a short dorsal 

 area, and has no trace of siphons or sessile apertures; the 

 margin is not reflected on itself as in Pecten ; there are two 

 rows of tentacular filaments springing from cord-like offsets 

 of the margin; the front one is furnished with very thick, 

 short, white, blunt cirrhi, disposed in a disorderly double line ; 

 the other is more within the shell, and has a simple series 

 of short, pale brown filaments of different lengths ; these are 

 rarely seen exserted, from the habitude of the animal to keep 

 the valves closed. The body, including the dark green liver 

 with the incorporated cream-coloured ovarium, proceeds from 

 the centre of the dorsal area on the anterior and posterior 

 sides of the great subcentral muscle, at which point it termi- 



