PECTEN. 301 



convex valve, where it laps over, and is not unfrequently 

 crovvnetl with fine dentated scales ; its entire length is 

 scarcely equal to one half the distance from the heaks to 

 the opposite ventral margin, which latter is strongly ar- 

 cuated, the most projecting portion of the lateral curva- 

 tures of the shell being (in the adult) rather above than 

 below the middle of the sides. The triangular callus on 

 either side of the cartilage in the under valve is large and 

 rather projecting. The colouring is very variable, it is fre- 

 quently of an uniform white, yellow, orange, red, brown, 

 or purplish pink ; with the under valve of a lighter 

 cast, and the interior whitish and more or less stained 

 with the external painting. Often, too, it is clouded or 

 variegated with two of these tints, as, for instance, with 

 undulating streaks of white on a dark pinkish red ground. 

 One of the most striking styles of painting is that ex- 

 hibited in the variety lineatus, where the snowy surface 

 of the valves is relieved in one or both of them by a dark 

 red line crowning the summit of all the costse. A beau- 

 tifully painted shell in our cabinet is speckled with snow- 

 white spots, edged below with chocolate-red on a ground 

 of crimson, with three of its ribs stained with brilliant 

 orange yellow. The diameter ascribed to the species by 

 the accurate Montagu, is " about two inches and a half ;" 

 but this is rather above than below the ordinary standard. 

 The length very slightly exceeds the breadth, except 

 in the young, where the converse prevails. The variety 

 Audouinii is by no means uncommon, and is usually mottled 

 or variegated, and of a darker colour internally than in the 

 typical form. We met with a young single valve of it 

 at Torquay, which, from the magnitude of its upper costal 

 squama}, and the imperfect developcment of its subsidiary and 

 interstitial scales, presented the aspect of a distinct species. 



