172 NEW-YORK FAUNA — MOLLUSCA. 



TAMIL Y PEC TWIDJE. 



Animal with a mantle, not adherent, open almost entirely in its whole circumference ; with- 

 out tube or peculiar opening ; always with the rudiment of a foot at the abdominal portion 

 {often canaliculated), which separates the two pair of gills. Shell in general subregular, 

 compact, with ribs or stria, diverging from the beaks, which are often eared. Hinge 

 variable, fixed either by a byssus or by one of the valves. 



GENUS PECTEN. Bruguieres. Turton. 



Animal orbicular, often thick and occasionally much compressed. Mantle margined with 

 one or two series of very fine filaments, among which are seen small pearly globules. Foot 

 small, conic, canaliculate, and generally with a byssus. Mouth surrounded by tentacular 

 appendages, branched and irregular, with a pair of triangular palpi on each side, truncated 

 at their extremities. Gills moderately large : termination of the intestinal canal somewhat 

 beneath. Marine. Shell free or fixed, often thin, somewhat orbicular, inequivalve, trans- 

 versely dilated into auricles : superior margin straight : beaks contiguous. Hinge toothless, 

 with a triangular internal pit for the cartilage ; a ligamentous membrane along the whole 

 length of the hinge. 



Obs. This genus is remarkable for the beautiful disposition of its colors in many of the 

 species. More than sixty living, and nearly as many fossil species, are enumerated in the 

 most recent publications. Several are used as food. 



Pecten concentricus. 



PLATE XI. FIG. 205. 



(STATE COLLECTION.) 



Pecten ccnceniriats. Say, Jour. Acad. Nat. Sc. Vol. 2, p. 259. 



P. id. Conkad, Amer. Marine Conchol. pi. 1, fig. 2. 



P. id. Gould, Invertelirata of Mass. p. 134, fig, 88. 



P. Un-olaris? Lamakck, An. sans vert. Ed. Brux. Vol.3, p. 52. (Young?) 



Description. Shell robust, suborbicular, with eighteen to twenty elevated rounded ribs, 

 and numerous concentric wrinkles equally on the ribs and interspaces : no longitudinal lines ; 

 one valve somewhat ventricose, the other convex. Auricles nearly equal, nearly straight on 

 one end, rounded or irregular on the other ; its surface with obsolete radiating lines. Liga- 

 mentary pit superficial, small. 



Color. Dusky horn-color, with white or yellowish or reddish concentric bands, most nu- 

 merous towards the beaks. In the young, one valve is pale yellow, banded with reddish, 

 brown or black ; the other brown or grey brown, occasionally brownish black. 



Length, 0-8 - 3-1. Width, 0" 9 - 3-5. 



