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