LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

04 LOWEB CBETACEODB DEPOSITS IN CALIFORNIA. AND OREGON
type as given by Stanton 0896, p. 14), show that the horizon not tower than Loner
Cretaceous (Valanginian). Among the associated speciea contained in bis list are
Amelia ernxzicallis, PeUen californicits, Cyprina oceidentalu Whiteavea, and Arro-
(eHint's i'mprMwa (Gabb). The locality is at the base of the Paskenta group; none
of the 18 species of this list are found in the Knosville senca (Tithonian) os here
restricted.
TertbraUlla denslconis (Anderson)
(Piatt 1, Spiral «, T>
/WifcmetanwJfo AHTJEKSON, Calif. Acad. Set., Pr,, 3d ser., vol. 2,1903, p, 72,
pi. 7, figs, 157, 168; Hometown and Texas Springs, Strata County,
Shell of medium ska, diameter II to IS mm.; trigonal, gibbous, when full grown,
the greatest thickness being near the middle; lateral margins straight, meeting at
aa angle of about 90 degrees at the beak; anterior margin broadly rounded; dorsal
valve more convex than the ventral, inflated; ventral valve flattened, rising ia front
in a pronounced sinus; anterior part of each valva bears angular or founded plication*
which disappear near the central part of the shell; surfaces of both valves bear fine
fltriations, best sees on the posterior half of the shell, The aimis on the ventral
valva bears three or four plications, denticulated on the margin; margin of dorsal
valve denticulated, the longer plications pointed and tooth-liko when seen from the
front; beaks not prominent; deltidium small; width of shell greater than the length.
This shell rMemblaa the northern forms, "Rhynehonella" gnajkapfiara Meek, and
"Jf." maudewis Whiteavee, although the latter appears to be relatively broader in
front.
Thin species ia not uncommon at Horsetown and Texas Springs, Shasta County,
ia the highest beds of the Horsetown group. Its horimn should be upper Albian.
Tcrabratctla w&ifcana (Anderson)
(Plito 1, ftpina i, i)
Rhyndwmlla IRWICANA AITDBIISQM, Calif. Acad. Set. Pr., 3d sor., vol. 2, 1002, p. 72,
pi, 7, figs. 160,161; Horsetown tod Texas Springs., Shastb County, California.
This shell differs from the preceding mainly in its finer sculpture and less prominent
plications and marginal denticulations. The ainus on the ventral valve possesses
about nine or ten plications and as many marginal denticles. It occurs with
the preceding, and is probably confined to the same horizon.
Tcrcbraltila ooitla Anderson, n. sp.
{Plata ». &gtma 17,13)
Shell small, ovate, longer than broad, convex, smooth and without ornamentation;
almost equivalve, the ventral valve extending a little behind the margin of the
dorsal valve; length of the ventral valve of the holatype, 20 mm.; width of ventral
valve, IB mm.; thickness, 11 mm.; front marked by only a faint median sinus in the
dorsal valve; surface of the shell smooth and silky.
The teletype (Calif. Acad. Sei. type Coll.) was found in the Neptune icma on
the east branch of Huleu Creek, locality 1659 (Calif. Acad. Sci,), associated with
Lytoceras neptunianum, Dounitleicsras mammillatum, var., i3swjarUic«roa breweri,
and many other species characteristic of the upper Horsetown (middle Albian) beds
of this district. Three good examples of the species were found here.