LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 213
The surface of the cast is nearly smooth, hut fragments of the shell show oblique,
relatively fine, rounded coatae, especially visible on the abaft; these arise on the
dorsal cone and slope forward toward the ventral zone which they cross without
interruption. The sapta are not perfectly shown on the genotype, but as they appear
on a large fragment Of fafairutfA nov. the first lateral lobe ia asymmetrically di*
vided, and its branches are divided in a similar manner. In form and ornamentation
the shell resembles the genotype of Dirrt/nweeras Hyatt {Ancylocertu simplex d'Orbigny),
but as no complete description Qf this genua has been found which shows its
relationship, generic identity cannot be claimed. Spath has included Dirrymacerat
in his Sateroceratidae, and it is possible that it may include "Heleroceras" tardieui
Kilian (1910, pi. 7). This form begins with helicoid early whorls, differing greatly
from those of Shaetacerae which show no tendency toward holieoid whorls.
Four apecies of this genus have been found, all of tham in nearly the same stratigraphic
zone, namely, in the upper part of the Horsetown group (lower Gargasian),
and all in the Cottonwood district, Shasta County, above the Mitchell zone, and a
little above the zone of Tropaeum percostatum (Gabb).
Shaetoceras eetlifornisttm Anderson, n. ap.
(Plata H, fliuro I; p]at« 73, firU* •)
In Gabb's attempted revision of "Crioceras" percostatus (Gabb, 1800a, p. 138,139)
he refers to the holotype of this species, now in the Museum of Paleontology, University
of California, giving its length as 17 Inehca. The shell is large, robust, or
massive, its general form being that of Ancylocerae. The early coil ia diseoidal,
crioceratid, slightly flattened on the dorsum; the shaft increases rapidly in section
after leaving tho early coil; shell costate, the small rounded costae being oblique,
arising in the dorsal lone and crossing the sides with forward inclination at an angle
of about IS degrees from the normal and also crossing the ventral zone without interruption
but with reduced strength. On the recurved limb of the croaier a few strong
rounded ridges, more prominent on the ventral aide, are developed; crosier cl-oscly
bent on the dorsal side, more broadly curved on the periphery; section of early
whorls broadly elliptical, that of the shaft more compressed; section of bucol limb
nearly circular. The holotype of the species has a length of 17.S inches and a width
across both limbs of the crosier of nearly 10 inches. The type locality and horizon
of this specimen are not definitely known, but the horizon of its known, congeners,
herein described, is In the upper part of the Horsetown group (lower Gargasian),
as found in the Cottonwood district, Shaata County, Many fragments of shells
belonging to this genus, but not to one species, have been found on Hulen Creek, and
on Mitchell Creek and Bearing River, a little above the zone of Tropaeum percasialtim,
and this is probably the horizon of the holotype of the present species.
Sfwstocsrae s has tense Anderson, n. sp.
(Plata 73, Stun 3; pints 73, filure 1)
This shell has the form of A neyloitras but is devoid of tubercules and Splnna,
such as character! le this genus. The aurfaec of tbe shell is smooth, although showing
faint rounded, oblique ribs, similar to those of the genotype; section of early whorl
and lower part of shaft flattened or moderately elliptical; section of body-chamber
more inflated; costae not conspicuous on the shaft, more pronounced on the early
coil; bucsl limb furnished with heavy transverse ribs, more prominent on the ventral
aide; section of bucal limb broadly elliptical, flattened on the dorsal border; dorsal
border of the shaft nearly straight. In form this species somewhat resembles ShastQcerm
catifamicum hut differs from it in some important rcspecta. The shell is