PECTEN. 53 



much distorted, which were attached by a strong byssus 

 as well as adhering by the shell. According to Fischer 

 the foot does not become atrophied or proportionally 

 smaller in the fixed adult, although it is then quite use- 

 less for the purpose of locomotion. This fact is opposed 

 to the general idea that the size of organs is modified 

 or affected by a change in the habits of an animal. The 

 present species was first described by Lister with his 

 wonted accuracy. Wallace, in his ' History of the 

 Orkneys/ has an ingenious way of accounting for the 

 shells being so distorted. He calls them the ' ' twisted 

 Pectines of Stroma," and says, " I cannot think the odd 

 strange tumbling the tides make there can contribute 

 anything to that frame ; yet after all I never see them 

 in any other place." 



It is the Ostrea sinuosa of Gmelin and the P. distortus 

 of Da Costa. In its younger state it is the P. multi- 

 striatus of Poli, and the P. Isabella of Macgillivray but 

 not of Lamarck. 



2. P. va'rius*, Linne. 



Ostrea varia, Linn. Syst. Nat. p. 1146. P. varius, F. & H. ii p 27.3 

 pi. L. f. 1. 



Body pale red, pink, brown, or yellow, sometimes mottled 

 with white or streaked with purplish -brown : mantle broad- 

 edged : cirri numerous, of unequal length but mostly long 

 and slender, arranged in four rows : ocelli about 30, black, and 

 smaller than in the last species : foot rather large, thick, and 

 white. 



Shell transversely oval, much broader in front than be- 

 hind, nearly equilateral, rather solid and slightly glossy : sculp- 

 ture, 25-30 smooth and rounded ribs, which are equal-sized • 

 the whole surface is also covered transversely with fine plates 

 which often form vaulted spines on the crests of the ribs j the 

 interstices of the ribs are marked with minute bifurcatino- 



* Variegated. 



