LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

218 lower cretaceotffi deposits in california and oRegon
Hamilea imilalor Anderson, n. sp.
(Plaus «, fipim 4, &}
A single fragmentary example of a hamitid species was found in the Perrin zone
at Locality 1688 (Calif, Acad. Sci.) in the upper part of the Horsetown group. It
Bcems to be closely related to Hamitea ormolus Sowerby, although it ia from a lower
stratigraphic horizon, here regarded as middle Albian. Aa far aa the species can be
described from this example, it has the following characters:
Shell large, tapering slowly, section of costate limb elliptical, rounded on both
dorsal and ventral borders; surface marked by numerous oblique, rounded ribs,
separated by wider interspaces, the interval being about 3 mm, broad; ventral zone
bordered on both sides by single rows of broad, low, rounded tubercules, which
appear upon each third rib, although their exact relation to the rib is not clearly
acen; septum aa seen in the figure, the lobes and their principal branches being bipartite,
in the manner of Xjftowai. The holotype (Calif. Acad. Sei. type Coll.)
has the following dimensions: length, 67 mm.; dorse-ventral diameter, at larger end,
43 mm.; transverse diameter, larger end, 31 mm,; same diameter at smaller end,
30 mm.
This spcciea has the general characters of Hamiita armatut Sowerby, as figured by
Boule and Thevenin (IGCKM.907, p. 5ft) especially with respec t to the suture line. The
holotype of the present apeciea was associated with AcantAopIiles ptrrini, Cleoniccras
{eewitei, Phylloeerat ihtresat, and iHplyckoccras lam Gabb, all of which are found
100 to 200 feet beneath the Xeptune zone in the upper part of the Horsetown group.
Ptychaceraa d'Orbigny
Ptychoctraa natriee Anderson, n. sp.
(Plata Bl, figure
Shell small or of moderate site having the two limbs folded closely together;
section of the two limbs subepiadr&te; smaller limb subcircular in section, nearly
smooth, tapering gradually; larger limb quadrate in section, slightly concave on its
dorsal contact with the smaller limb; costate, with gently inclined, simple costae
crossing the ventral tone as smooth rounded ridges; ventral zone rounded; septa not
exposed on holotype. The species belongs to the group represented by Piychoceras
puioirianum d'Orbigny, found in the Neocomian (Barremian) of Franco, which is its
nearest known analogue. The holotype (Calif. Sci. type Coll.) was found in
the Mitchell zone at Locality 1657 (Calif. Acad. Sci.) on the west branch of Mitchell
Creek, a mile above the mouth of this stream. It has the following dimensions:
total length, AS mm.; transverse measure (both limbs), 24 mm.; height of aperture,
13 mm.; width of aperture, 13 mm.; top of crosier roundly curved. This example
was found associated with SkaaticrioccTaz ponienie, Paeudocrioecras ap., and tnoceramus
ovatoidea nov., in strata regarded as upper Barremian in age.
Diptychoceras Gabb
Diplychoccroe laepc Gabb
Diplychoeeraa JAM'S GABB, Paleont. Calif., vol. 2, 1869, p. 144, pi. 25, figs. 21, 21a,
21b; "Shasta Group," Cottonwood Creek, Shasta County.
Gabb's account reads in part aB follows:
"Shell moderate in site, limbs long and slender, section of the smaller limb subelliptical,
slightly flattened on the ventral (dorsal) side; second limb subcircular,
very slightly emarginate by the encroachment of the preceding branch; last limb
suddenly incurved, and extending to (or beyond ?) the middle of the shell. Surface