114 CALIKOHNIA ACADEMY OK SC1KNCE8. 



[S. D.J Pecten (Plagioctenium) subventricosus Dall. 



PecUn ( PlagiocUnium ) suhvcntricoms Dall, Trans. Wagner Insi. Sci., Vol. Ill, Part 4, 1898, 

 p. 707. PI. XXIX, fig. 8. 



"Shell of the type of P. venlricosus Sby., from which it diflcrs by being smaller and less 

 tumid, less e.xpanded laterally, with the ribs rounded, instead of flattened, above, and with narrow 

 interspaces ; the tops of the ribs smooth, the sides with a tiense fringe of concentric lamella;." (Uall). 



Dimensions. — Long. 65 mm.; alt. 65 mm.; diam. 24 mm. 



Sevenil speciiuciis of this species were found in ilie Pliocene of Pacific Bead), 

 near San Diego. 



Pliocene. — Veiittira County (Bowers): San Diego (Hemphill; Stearns; Arnold). 



35. Pecten (Plagioctenium) ventricosus Sonxrhy. 



1'i.ATE XI, Fuis. 3, 3n, (> .*ni> (i»i. 



Pecten ventricosus SuY., Thes. Conch., Pecten, 1843, p. 51, PI. XII, figs. 18, 19. Gabu, Pal Ca!., 

 Vol. II, 1869, p. 104. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 258. = P. lumidus 

 Sby., 1S35 (not of Turt., 1S22, nor of Zeiten, 1830) ^ P. circutan's Shy. {ex parte) 

 = P. inca dOrb., 1847 Ui<^^ Dall., Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, 

 p. 710). 



Shell thin, orbicular, with subequal inflated valves which are subequilateral ; uniformly 

 radiately ribbed; about twenty-two strong, angular, even ribs separated by narrow interspaces; the 

 whole surface covered with fine, sharp, concentric, looped lamellae, which e-xhibits the oblique growth 

 in adult shells; ears moderately small, nearly equilateral in left valve; byssal notch prominent; surface 

 of ears ornamented with fine concentric lamcllre of growth, and sometimes with radiating ridges. 



Dimensions. — Long. 59 mm.; alt. 50 mm.; diam. 32 mm.; hinge 31 mm.; angle of dorsal 

 margin 1 10 degrees. 



P. i.tquisulcatus Carpenter resembles this species very closely, but is thinner 

 and flatter and has narrower ribs. Probably all the Pleistocene forms would come 

 under the head of P. ventricosus, but many of them have been labeled P. 'ttpii- 

 sulcalus. Speciiuens identified by Dr. Dall. 



Figures G and (m, Plate XI, represent a shell which wa.s found in the 

 upper San Pedro series at San Pedro, and which is probably a variety of P. 

 ventricosus. 



Very common in the upper San Pedro series of San Pedro, Long Beach, Los 

 Cerritos, Crawfish George's, and Deadman Island. Found also in Pleistocene on Old 

 Mission ditch, north of Ventura, and in the Pleistocene at Twent3--sixtli Street. San 

 Diego. The specimen figured is from the upper San Pedro series at San Pedro, and 

 is now in the collection of Delos Arnold. 



Living. — Santa Barbara to west tropical America (Dall). 



Pleistocene. — San Pedro; San Diego; Lower California (IIem|ihill; Stearns; 

 Orcutt: and Cooper): San Pedro; Ventura; San Diego (Arnold). 



