PANAMIC-PACIFIC PELECYPODA 163 



This is typically a cold-water scallop of the Humboldt Current and 

 attains its best development along the coast of Peru southward from the 

 Bay of Sechura. More northerly records are questionable. In Peru, it is 

 a highly esteemed seafood, commonly appearing in the markets of Lima 

 by the name of "senoritas". As fossil, it is plentiful in the Peruvian 

 tablazos and in those of southern Ecuador. Grant and Gale considered 

 certain fossil Pectens from the Pliocene of southern California as subspecies of 

 purpuratus. A. purpuratus is strikingly similar to members of the A. eboreus- 

 solarioides group from the Miocene and Pliocene of Florida and the south 

 Atlantic states. 



Range — Coastal waters of Chile and Peru northward to Paita and 

 Sechura. 



Aeqnlpect«n (Plagioctenium) clrcnlaris (Sowerby) Plate 19, figures 2-2b 



Pecten tumidus Sowerby, 1835, Proc. Zool. Soc. London, p. 109. Not P. tumidus Turton 



1822, nor Zeiten, 1830. 

 Pecten circularis Sowerby, 183S, Proc. Zool. Soc. London, p. 110 (Guaymas). — Sowerby, 



1842, Thes. Icon., vol. 1, p. 51, pi. 12, fig. 23.— Re«ve, 1852, Conch. Icon., vol. 



8, Pecten, pi. 31, fig. 137. 

 Pecten (Plagioctenium) circularis Sowerby, Arnold, 1906, U. S. Geol. Survey, Prof. 



Paper +7, pp. 125, pi. 42, figs. 3, 4. 5, 6; pi. 44, figs. 6, 6a, 6b, 7.— Hertlein 



and Strong, 1946, Zoologica, vol. 31, pt. 2, pp. 57, 58. — Hertlein and Strong, 



1955, Bull. Araer. Mus. Nat. Hist., vol. 107, art. 2, pp. 179, 180. 

 Pecten (Aequipecten) gibbus (Linnaeus) variety circularis Sowerby, Grant and Gale, 



1931, Mem. San Diego Soc. Nat. Hist., vol. 1. pp. 218, 219. 

 Pecten ventricosus Sowerby, 1842, Thes. Icon., vol. 1, p. 51, no. 19, pi. 12, figs. 18, 19, 



26. (New name to replace tumidus). — Reeve, 1852. Conch. Icon., vol. 8, Pecten, 



pi. 7, figs. 31a, b. 



Valves Strongly and nearly equally convex, the average size from 45 

 to 60 mm. Ribs 20 to 22; in the left valve, the ribs are low, rounded, be- 

 tween narrowly grooved interspaces while in the right they are higher, 

 rectangular to subtriangular, their sides somewhat bevelled, their inter- 

 spaces deep; both ribs and interspaces crossed by looped concentric threads. 

 Submargins somewhat flattened and plain. Color is variable, often brilliant, 

 ranging from plain white, pink, orange, brown, but more often lilac or 

 mahogany brown, generally more or less mottled. The right valve is usually 

 white within, the left often stained with brown. 



This is the common Pecten in Panama and along the northwest coast 

 of South America. In some localities it is quite plentiful. Fossil forms found in 

 the Pleistocene and Pliocene beds of Ecuador and northern Peru attain 

 a much larger size than their Recent representatives. 



Most recent authors consider A. circularis and A. ventricosus as one 

 species, the distinctions between them, if any, too slight for consistent 

 separation. Typical A. ventricosus from the Santa Elena Peninsula is a 

 rather solid shell, the adductor scar somewhat impressed and the fluted 

 ribs show only for a narrow zone around the inner margin. Specimens from 

 Sechura in the Paita Buffer Zone have a much thinner shell with the ribs 

 showing plainly inside well into the umbonal cavity. These shells are some- 

 times difficult to distinguish from half-grown A. purpuratus but have 



