LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

DESCRIPTION OF SPECIES 109
PxcnmvA* Lamarck
Pesttn Mailer
Pecten umplexicatta Gabb
P«ef«n eempJ*:nVo»K» GABB, Paleont. Calif., vol. 2, 1809, p. 199, pi. 33, fias. 97, &7aj
"Shasta Group," Morgan Valley, Lake County—STANTON, U. 3. Geol, Surv.,
Bull. 133, 1896, p. 37, pi. 2, figs. 7-9; Wilbur Spring?, Colusa County—ANDER-
SON (in LAWSON), U. 3. Geol. Surv., San Francisco Folio, 1014, p. 8; Berkeley
Hills, Contra Costa County,
This shell is of moderate size, thin, equivalve, neatly equilateral; aidca and base
forming a regular curve; shell slightly elongated; surface marked by about 12 to
14 radiating ribs, with aoraetimca on equal number of intermediary ribs. The length
of tbe holotype, about 57 mm.; width, 50 mm.
Gabb states that it is common in the limestone of Morgan Valley, Lake County,
Stanton found it in the limestone south of Wilbur Springs, Colusa County, and it
occurs in tbe Berkeley Hills, associated with Afrciiua h'ratas Gabb, and with other
well-known species characteristic of the Paskenta group.
Pecten californicut Gabb
Pecten Mlifomicut GABB, Paleont, Calif., vol. 1, 1884, p, 201, pi. 31, fig. 270; Cottonwood
Creek, Shasta County, California—STANTON, U, S, Geol. Surv., Bull. 133,
188£, p. 30, pi. 2, fig. 10; Cold fork of Cottonwood Creek, Tehama County.
This small species of Pecten occurs in both, the Pfwkenta and Hor&ctown groups,
and both north and south of the delta area on the west border of the Sacramento
Valley. Gabb seems to have confused this species with another occurring in the
Chico scries, giving the horizon of its occurrence as "Chico or Shasta group," Cottonwood
Creek. It has not been seen by tfca writer in the Cbieo series; Stanton
reported it from "near Stephenson's on the Cold fork of Cottonwood Creek, in beds
near the base of the Paskenta group, of the Shasta series, where it occurs with many
other species listed by bun (Stanton, 1395, p. 14). The same species has been found
abundantly in the lower part ol the Hor&ctown group on McCarthy Creek, a quarter
of a mile west af the Lowry Road.
Syncycl&nema Meek, 1&64
Syrtcydomma operculiformii (Gabb)
Pttlen Qpervutifttrmit GABB, Paleont. Calif., vol, 1, 1854, p. 201, pi. 28, fig, 188:
vol. 2, 1809, p. 200, 251: Cottonwood and Hulcn-crceks, Shasta County, ana
Curry's near Mount Diablo—STANTON, U. S, Geol. Surv., Bull. 133, 1895,
p. 16, 18, 32, 37; regarded aa occurring in both Shasta and Chico series—
STEWAJST, Phita. Acad. Nat. ScL, Spec, Publ. no. 3, 1930, p. 120; locality not
given.
The simple form and unomamentcd character af this shell has made its specific
description difficult. It is flatty lenticular, subcircular in outline below the auricles;
interior of the shell silky in texture, smooth, or polished without, but showing fine
concentric lines of growth; left valve with nearly equal auric]ea, right valve less
well known. The holotype ("tcctctypa" of Siewart) is in the Museum of Paleontology,
University of California. It has the following dimensions ; length, 22 mm.;
height, 20.5 mm.; thickness, about 3 mm. Similar forms are found in many parts
of the Shasta series, and for this reason tbe range of the species ia not definitely
known.