Pecten.] PELECYPODA. 873 



Fani. PECTINIDJE, Lamarck. 



Animal having an elongated, tongue-shaped, byssiferous foot ; the 

 ocelli are numerous and well developed ; hermaphrodite or dioecious. 



Shell inequivalve, inequilateral, auriculate, mostly closed, mono- 

 myarian, usually free ; area amphidetic or obscure ; ligament obsolete 

 externally, the immersed portion forming an internal resilium ; hinge 

 with a few lamelliform divergent and symmetrical teeth, mostly feeble 

 or not developed. 



Silurian to Recent. 



Genus 1. PECTEN, Muller, 1776. 

 Pecten, Muller, Prodr. Zool. Dan., 1776, 248. Type : Ostrea maxima, L. 



Animal having the labial palps pectinated within, the liver arbor- 

 escent, branchial leaflets equal, semicircular, rectum and anus free 

 and extending beyond the adductor muscle ; muscular system asym- 

 metrical ; tentacular filaments of the mantle elongated ; byssal gland 

 more or less developed. 



Shell suborbicular, auriculate, ornamented by radiating costae ; 

 right valve typically convex, inflated and produced in the umbonal 

 region, which curves inwards ; left valve typically flat, and smaller 

 than the other, but in certain sections of the genus it is subequal and 

 convex ; cardinal line straight ligamental pit commonly triangular, 

 internal. 



Distribution. World-wide in numerous species. 



Fossil in the Secondary and Tertiary. 



Vernacular Name. Scallop. 



KEY TO SUBGENERA. 



A. Shell usually rather large ; the right valve convex, the left 



flat ; ears subequal . . . . . . . . PECTEN. 



B. Shell of medium size ; both valves convex ; ears unequal . . CHLAMYS. 



C. Shell small, thin, translucent, with predominant concentric 



sculpture.. .. .. .. .. .. PSEUDAWUSIUM. 



Subgen. 1. PECTEN, s. str. 



Right valve moderately inflated, left valve flattish ; sculpture of 

 strong ribs with radial striation, more or less roughened by simple 

 concentric lamellation or incremental sculpture ; ears subequal. 



Sect. 1. EUVOLA, Ball, 1898. 



Euvola, Dall, Trans. Wagner Free Inst., iii, pt. 4, 1898, 694. Type : Pecten 

 ziczac, L. 



Right valve extremely inflated, surface polished, ribs moderate or 

 obsolete, without radial striation, concentric sculpture inconspicuous ; 

 left valve with or without conspicuous radial and concentric sculpture, 

 flat or concave. 



