LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

98 LOWER CHETACEOUS DBPOfllTa IK CALIFORNIA AJiD OHEOON
named by Stanton, which also includes Aucella craeeicolli* and "Btlemnilee" impretta
Gabb. Its etratigraphia position and relations have already been discussed, and its
association with the last-named species establishes its Paskenta age.
PIHSIBAB Meek
Pt'nna Linnaeus
Pinna ponfioa Anderson, n. sp.
(Flat* t, figvn 2)
Shell small, rather stout, slightly curved, tapering to an acuminate point; scction
of shell rhomboidol, dorsal and ventral borders thin; sides angulatod, but showing
a distinctly raised ridge; basal margin rounded, divided at the median Una of tbe
side; surface marked by nearly parallel longitudinal ribs on the dorsal part of the
shell, separated by wider interspaces; ventral part of the shell bearing two longitudinal
ribs parallel to the median ridge, below which are oblique undulations arising
at the ventral border and extending upward and toward the base, meeting the ribs
beneath the median line; apical angle about 33 degrees. The surface ornamentation
of this spacics is not unlike that of Pin no ealamiUnde* Shumard, ns figured by Whiteaves,
but in size and in the apical angle there is much difference.
The holotype (Calif. Acad. Sci. type Coll.) was obtained at Locality 1353 (Calif.
Acad. Sci.) near the bridge on the North fork of Cottonwood Creek, in the Ono zone
of the Horsetown group. It affords the following measurements: total length, 68
nun.; greatest width, 35 mm.; thickness at baso, 20 mm.
The holotype was found associated with Iwceramta calimic-uji, Aeroteuthis kemenst's,
and Neocrtitpcditti aguila nov., all of which characterize the zone. This appears
to be the oldest known species of Pinna in the Cretaceous of the West Coast capable
of description, although Stanton (1B95, p, 49, 92) mentions a small form, possibly
an immature specimen, found on the Shelton ranch, in beds here referred to the
Paskenta group, and therefore lower in the series.
Pinna tgutvtiiana Anderson, n. sp.
(FUt* i, flrure 1)
Shell of medium size, elongate, tapering to a near point, moderately thick, borders
not straight; cross section rbomboidal, margin acute, sides slightly curved; valves
divided near the middle by an angulated ridge (124 degrees), extending from apex
to base; dorsal side of valves narrower than tbe ventral; borders of shell slightly
bent, doreal eoncavely, ventral convesly: surface of derail part marked by BVX or
seven narrow, subparallel ribs, separated by broader rounded interspaces; ventral
portion showing eight or nine such ribs and interspaces; these are crossed obliquely
by a few faint undulations; apical angle about 33 degrees.
The holotype (Calif. Acad. Sci. type Coll.) was found at Locality 1698 (Calif.
Acad. Sci.), in the Perrin zone, where: it was associated with Acanlhopltiee perrini,
JSonneratia rogersi, and Phylloccrat thereeae nov. It has the following dimensions:
total length, 144 mm.; greatest width, 70 mm.; greatest thickness, 40 mm.
This species has bitten obtained at three separate localities on Hulen Creek—
Localities 152, 1659, and 1608 (Calif. Acad. Sci.). It differs from all the spcciei
known from the later Cretaceous of the West Coast chiefly in its apical angle, its
cross section, and in the manner of its surface ornamentation. The stratigraphical
range of the species is apparently confined to the Hulen beds, although it may be
found to range lower.