PANAMIC-PACIFIC PELECYPODA 155 



Range — Gulf of California to Ecuador. Colombia: Isia la Gorgona. 

 Ecuador: Coast between Punta Blanca and Puerto Callo; Santa Elena. 



Pllcatula spondylopsis Rochebrune 



Plicatula spondylopsis Rochebrune, 1895, Bull. Mus. Nat. Hist. Paris, vol. 1, p. 242 

 "Laguna des isles de San Jose, Gulf of California". — Lamy, 1939, Jour, de 

 Conchyl., vol. 83, No. 1, p. 23. — Hertlein and Strong, 1946, Zoologica, vol. 31, 

 pt. 2, pp. 63, 64, pi. 1, figs. 15, 16. — Durham, 1950, Mem. Geol. Soc. America, 

 No. 43, p. 69, pi. 15, fig. 2 fossil, Lower California. 



Plicatula ostreivaga Rochebrune, 1895, op. cit. p. 242. 



Shell roughly trigonal in shape, thick, ornamented by coarse radial 

 plaited sculpture, which, however, may be partially or almost wholly absent 

 on some specimens; two hinge teeth in each valve. In perfect shells the 

 exterior is colored purple and the interior white, with dark spots around 

 the corrugated margin. Muscles scar nearer the posterior margin. A very 

 narrow space is occupied by the animal. — (Hertlein and Strong, 1946.) 



Differs from P. penicillata by its smaller area of attachment, usually 

 thicker, vaulted shell, and strong ribs. Some specimens of Plicatula in the 

 U. S. National Museum, probably belonging to this species are sharply 

 plicated and resemble P. gibbosa Lamarck of the Western Atlantic. 



Range — Gulf of California to Ecuador and Galapagos. 



Plicatula anomioides Keen 



Plicatula anomioides Keen, 1958, Bull. Amer. Paleont., vol. 38, No. 172, p. 241. pi. 31, 

 figs. 4, 7, 8. 



Shell nearly circular in outline, white, thin, with faint divaricating 

 radial ribs, especially near the beaks; interior shining white, with, on most 

 specimens, one or more greenish blotches. Lower valve firmly cemented to 

 substrate and, therefore, tending to reproduce the irregularities of its 

 surface. Hinge strong, with two serrate crura in either valve, difficult to 

 disengage without damage to the shell. Coalesced adductor muscle scars 

 large and slightly posterior to a line drawn vertically through the beaks. 

 (Keen, 1958.) 



Range — Guaymas, Mexico. 



Family PECTINIDAE 



Shell monomyarian or provided with a single adductor muscle, the 

 scar of which is placed slightly posterior of the middle. Valves subcircular, 

 subtriangular, equilateral or nearly so, the beaks and umbones placed 

 medially, usually with the dorsal submargins below the hinge line, deeply 

 impressed forming triangular wings or ears, the anterior ear of the right 

 valve often cut into by a deep byssal notch. The two valves may be alike 

 in shape, convexity and sculpture, or they may be quite different; in the 

 latter case, the right valve is larger, more convex, the left valve flat and 

 depressed. Surface may be sculptured with large, strong ribs which corrugate 

 the ventral margins, or the surface may be practically smooth or with con- 

 centric markings only. Hinge line straight edentulous or with strong crural 

 elements and sometimes striations. Ligament is mainly attached to a resllifer 

 in the shape of a central triangular pit below the beak. The surface of the 

 shell often colored, the pattern highly variable. 



This family contains the scallops or Pectens, a large and important 



