PANAMIC-PACIFIC PELECYPODA 159 



is shown in the reverse, mostly around the margin but the flutings of the 

 ribs are shallow and do not indent the margin. Color of the valves is mostly 

 wine-red, the umbones, especially of the right valve much lighter, some- 

 times white. Left valve is generally maculated more strongly than that of 

 the right. The interspaces on the right valve generally finely speckled with 

 white dots. Interior mostly white, except in the umbonal cavity which may 

 be yellow and for a small, narrow, colored margin in the right valve; not 

 developed in the left. 



Length 34.6 mm., height 3L5 mm., diameter 10.7 mm. double valves, 

 length of hinge line 18 mm. Venado Beach, Canal Zone. 



Length 40.05 mm., height 37.8 mm., diameter 24.3 mm. right valve. 

 Santa Elena, Ecuador. 



Length 38.7 mm., height 34.1 mm., diameter 5 mm. left valve. Man- 

 glaralto, Ecuador. 



This small species has often been confused with the much larger Pecten 

 vogdesi Arnold and perhaps most, if not all, records of P. vogdesi from Pan- 

 ama southward may be based on this species. In addition to its much 

 smaller size and lighter texture, Pecten perulus differs by its lower convexity 

 of the right valve, its lower umbone which does not rise above the hinge mar- 

 gin and by its sulcated or mesially grooved ribs. The left valve differs by its 

 wider, more flaring submargins and especially by its narrower ribs, and much 

 wider interspaces, each carrying an intercalary riblet. 



Local but well distributed from Panama southward to northern Peru. 



Range — Panama south to northern Peru. Panama: Guanico. Canal 

 Zone: Venado Beach. Ecuador: Santa Elena; Manglaralto; Canoa; Manta. 

 Peru: Mancora; Caleto Mero; Lobitos. 



Subgenus FLABELLIPECTEN Sacco, 1897 



Type species by original designation and tautonomy, F. jlabellijormis 

 Rrocchi. 



Shell generally large or of medium size and of medium weight. Right 

 valve weakly to moderately convex, the left valve flat with arched sub- 

 margins and flattened or depressed beak and umbone. The sculpture is 

 commonly formed by rather numerous low ribs, rounded in the right valve 

 and spaced between narrower interspaces, while the ribs of the left valve 

 are narrower, their interspaces somewhat wider and often showing an 

 interstitial thread or riblet; in addition, the whole surface is thickly over- 

 run by concentric threads looped over the top of the ribs and across the 

 interspaces; on the left valve, the concentric threads are heavier and show 

 especially well in the interspaces. Ears are subequal in size and shape, the 

 byssal gap small. Hinge area carries strong crura, the right valve having 

 two crural teeth on each side of the ligament pit or resilifer, the left valve 

 with one only, the surface of the crura being finely wrinkled. Interior with 

 the radial flutings extending about a third of the way in from the margin. 



This is an important fossil group in rocks of Miocene age. It is repre- 

 sented in Panama and Costa Rica by Pecten gatunensis Toula and Pecten 

 macdonddi Olsson. Closely allied to these species in the Recent fauna are 

 Pecten sericeus and its close relative P. diegensis Dall of Californian waters. 



