PECTEN. 73 



of Dr. Gray but not of Chemnitz) resembles the present 

 species in nearly every respect but that of size. It 

 may be an arctic variety of P. similis or (more probably) 

 a direct and f pur-sang ' descendant from the original 

 stock. 



B. Upper valve nearly flat and concave towards the beak : 

 hinge-line ribbed obliquely. 



^?7^ 9. P. MAx'iMus*,(Linne.) ^. 1^ 



Ostrea maxima, Linn. Syst. JS"at. p. 1144. P. maximus, F. & H. ii. p. 296, 

 pi. xlix. 



BODY pinkish-white above and bright red or pink in front : 

 mantle variously marbled with brown, black, and white : cirri 

 on the inner margin of the mantle short, white, and arranged 

 in a single row ; those on the fixed or exterior margin are of 

 different lengths and arranged in three irregular rows : ocelli 

 of a greenish- blue or purplish hue, forming two rows, and 

 numbering from 30 to 35 ; those in the front row are con- 

 siderably larger than the rest, and correspond with the ribs of 

 the shell : foot snow-white, short, grooved, with a spatulate 

 extremity. 



SHELL nearly circular, except behind, where the projecting 

 ears give a square outline, equilateral above and nearly so 

 beneath ; upper valve slightly raised in the middle, and 

 smaller than the lower valve, which is very convex ; it is thick 

 and solid, glossy in the umbonal region but elsewhere of a 

 dull hue : sculpture, 15 or 16 ribs in each valve, which radiate 

 from the beaks, and are strong, and nearly as broad as the in- 

 terstices between them ; the ribs and interstices are scored by 

 a few parallel striae, which are more numerous on the lower 

 than the upper valve ; the whole surface is covered with 

 minute and close-set thin concentric plates, which are im- 

 bricated or overlap one another like roof-tiles : colour reddish- 

 brown on the upper valve, with a yellow tint on the lower 

 valve ; both valves are sometimes beautifully mottled or marked 

 with bands, zigzag streaks, and spots of burnt umber, or bright 

 yellow suffused with a delicate pink hue ; occasionally, but 



* Largest. 



