LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

DESCRIPTION Of BPECIE8 111
Shasta County—ST AJTTON, 17. S. Oeol. Surv., Bull, 133, 1885, p, 18; tbe species
ia included in a list from the lower Horsetown beds in the Cottonwood district,
Shasta County.
Gabb's description is in part as follows:
"Shell variable, usually tomewbat curved. Lower valve attached by a portion
of the surface, deep, radially costate, ribs occasionally dichotomous. Lpper valve
flat or concave, plicate like the lower, but not so strongly, ribs being sometimes
obsolete. Hinge robust; muscular scar large; internal margin of the upper valv«
crenato [crenulatedj; lower valve marked with pits corresponding to the teeth
above," Average length of the shell is about IS mm.
This species is characteristic of tbe lower Horsetown beds, and has not been found
by the writer in the Chico series, as might be thought likely From Gabb'a note as
to its occurrence on Battle Creek.
Plicalvla onfleiwi* Anderson, n. sp.
(PJita 4, fiitifte 1. 2, 3}
Shell small, semi-triangular, very inequivalve, often concavo-convex; lower valve
more convex, showing little evidence of attachment; surface highly convex, ornamented
by S to 12 sharp, radial ribs, some of which bear scale-like spines where
intersected by the strong lines of growth; upper valva usually concave, or flattened,
ornamented by 6 or more radial rounded plications.
The holotype (Calif. Acad. flei. type Coll.) was found on the North fork of Cottonwood
Creek, BOO feet above the bridge at Ono. Tbe spccies is also abundant in the
upper beds of the Paskenta group, and has been found at Locality 113 (Calif. Acad.
Sci.), 4 miles southwest of Ono, where it occurs about 000 feet beneath the lowest
beds assignable to the Horsetown group. It occurs hero associated with Poluptyekilta
ihaaltnsis, HOT. and Crioeeros cf. LOTAM Gabb.
LIMIDAB d'Orbigny
Lima Bmguifcrc
Lima ffiu