PECTEN. 71 



an inch long, and a trifle more than nine-tenths of an 

 inch in breadth. The striae in the present species are 

 raised and irregular ; and they are never punctured or 

 reticulate. In the other species the strise are sunk or 

 impressed and regular, and they are strongly punctured 

 or reticulate. The different substance of the shell, the 

 style and intensity of coloration, and the comparative 

 size of the left ear of the upper valve are also notable 

 marks of distinction. Even the fry of each species ex- 

 hibits its own peculiar characters. 



It is the P. fuel of Gmelin, P. reticulatus of Chem- 

 nitz, P. Landsburgi of Forbes, and P. aculeatus of my- 

 self. 



8. P. si'MiLis*,(Laskey) 



P. simiJis, Lask. Mem. Wern. Soc. i. p. 387, t. viii. f. 8 ; F. & II. ii. p. 293, 

 pi. lii. f. 6, and (animal) pi. S. f. 1. 



BODY very variable in colour, often pale yellow or whitish 

 with brown streaks and blotches : mantle fawn-coloured with 

 patches and lines of orange and black : cirri short ; some are 

 white and others brown, a few being thicker and longer than 

 the rest and mottled with milk-white : ocelli 6-8 in front and 

 nearly twice as many in a second row behind ; the former are 

 comparatively larger, pearly, and ringed with jet : foot of a 

 brilliant orange-colour or white. 



SHELL nearly circular but expanding towards each side, 

 where it forms an obtuse angle, and rhomboidal behind in 

 consequence of the projection of the ears, equilateral, de- 

 pressed, extremely thin and rather glossy ; lower valve con- 

 siderably smaller than the other, and to some extent enclosed 

 within it : sculpture, fine and close-set concentric lines only : 

 colour yellowish or milk-white mottled with reddish-brown 

 or flake-white spots or streaks, and often marked by longi- 

 tudinal white rays or transverse zigzag lines of a Yandyke 

 pattern : margins very thin, semicircular in front and sloping 

 about halfway on each side at an angle of 45 degrees to the 

 beaks ; byssal slope not toothed or serrate : beaks small but 



* Like the fry of P. maximus. 



