102 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



"iventricosus van aequisulcatus Carpenter in synonymy.] ". . . as 

 aequisulcatus, Santa Barbara, Calif., to Cape San Lucas, Lower 

 Calif. (Dall, 1921)." [Figured specimen = C. circularis aequisul- 

 cata (Carpenter).] 

 Pecten (Aequipecten) circularis aequisulcatus Carpenter. Keep, 1935, p. 



52, fig. 23. 

 Chla/nys (Aequipecten) aequisulcatus Carpenter. Bavay, 1936, p. 314. 

 Plagioctenium circularis aequisulcatus Carpenter. Morris, 1952, p. 16, 



pi. 1, fig. 5; pi. 5, fig. 1. 

 Plagioctenium circularis aequisulcatum (Carpenter 1865). Fitch, 1953, 

 p. 42, fig. 8. "Monterey Bay, California, to Cape San Lucas, Baja 

 California." 

 Pecten (Plagioctenium) circularis aequisulcatus Carpenter. Palmer, 

 1958, p. 71, pi. 3, figs. 1-3. "The types of this species consist of one 

 left valve, marked "type," and one double specimen, in the U. S. 

 National Museum, no. 15645, with the label "San Diego." [Under 

 Pliocene Palmer cited Grant & Gale, 1931, but in that paper 

 Pliocene records were given only for P. circularis Sowerby.] 

 Syntypes: U. S. National Museum. 



Type locality : San Diego, California. Syntypes so labelled, fide 

 Palmer, 1958, p. 71. 



Original description (Carpenter, 1864, p. 645) : Thinner and 

 flatter than ventricosus, with narrower ribs. 



Subsequent description (Carpenter, 1865, p. 179) : P. testa P. 

 ventricoso simili, sed tenuiore, minus ventricosa; costis pluribus angus- 

 tioribus xx.-xxi. ; interstitiis (praecipue valva superiore) fere aequalibus; 

 auricuHs magis productis, acutis ; sinu serrato ; testa jun. interstitiis alte 

 insculptis, laminis concentricis crebris, vix extantibus, interstitia, costas 

 auriculasque transeuntibvis. Long. 3.2, lat. 3.35, alt. 1.5. 



Additional descriptive notes: This subspecies is the northern form of 

 the typical and can be distinguished primarily by its thinner shell, flatter 

 left valve and more subdued coloring. In adult specimens the ribs are 

 more angulate than those of the typical and the concentric lamellae of 

 the disk more prominent. The size of mature specimens is greater, the 

 average height being 80 mm and the length 88. The author's collection 

 contains a specimen from San Pedro measuring 98 mm in height and 

 106 in length, the largest for which any record could be found. Adult 

 specimens are dark brown or red-brown, mottled with white or yellow; 

 occasional juveniles are almost completely white, others red-orange or 

 yellow and with white or brown mottling. 



I 



