LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description OP 8pecteb 215
Mitchell Creek, in all cases about ISO to 250 feet above tbe Argonaut zone, it may be
assumed that its horizon ia in the upper part of the Horsetown group (lower Gar»
gosian) in the Cottonwood district, Shasta County. The specics is not known from
any other district.
iSJtiisioMraw insnirieewtim Anderson, n. Bp.
{Ftst® 17, Spirt 1)
In the collections of the California Academy of Sciences there ia a body-chamber
of an example representing this genua which possesses some striking features not seen
in any of the preceding forms. It represents a mature shell with a much-inflated
crosier, although the adjacent parts—namely, the recurved limb and the part of the
shaft still remaining—are contracted, especially at and about the aperture, where
it allows a few stout ribs, well developed on the outer border. In section the buesl
limb ie nearly circular rather than elliptical. Thia specimen ia the holotype of the
present species (Calif. Acad. Sci. type Coll.). It haa the following dimensions:
the ventricoBe crosier has a maximum circumference of 20.3 inches and a maximum
diameter of €.5 inches; greater diameter at the position of the Laat septum, $ inches,
lesser diameter, 3.3 inches; diameter at end of bucal limb, 4.1 laches; estimated
length cf complete shell, about 11-5 inches. The suture line is not shown but is
supposedly not unlike that of S. behemoth. This specimen was found on Hulen Creek
in the none of the preceding spcciea, some 200 feet above the Argonaut zone. Fragments
cf the species are not uncommon on the west branch of Hulen Creek, but none
have been, found farther south.
Hamiticer&e Anderson, n. genua
Many smaller aneyloceratid forms have been found in the Aptian strata in California
and in other countries,, which it seems desirable to unite under a new generic
name. Among the number obtained in California by Gabb he included at least three
apecies under the name "Hrficanajltie" aeqweostatus, but no satisfactory diagnosis
of any of them was given. As shown in another place, the name Heli'caneyitM properly
attaches to only one of these apocies. To this genus the other forms here mentioned
cannot he shown to have close relationship, and for them the name Hamiticerae
seems to he appropriate and is suggested for the group. The forms here placed under
it have the outward aspect of ffamiie* Parkinson (a. ».), but they possess distinctly
tubercul&te riba, and like Hamitidae seem to have originated in a hoplitid (possibly a
parahoplitid) stock. However, in the possession of tuberculste ribs, they differ
much from true /faroites and from other types included in Hamitidae, as restricted
by Spath,
The trituberculate riba of the genotype, II. pikbryi nov,, and the tripartite lobes
of the septum seem to place them clearly among the Ancyloeeratidoe, as emended by
Whitehouse. In some characters, namely, in ribbing and perhaps in form, they may
represent a development somewhat parallel to that of Farancyloceraa Spath; among
them the ribs on the smaller limb, at least, poas&ss two or three rows of tubercules
similar to those of ancyloceratids. The group appears to include "Ancyloteraa"
poto^ontatm Stolley and perhaps also "Ancyloeeros" obovatum von Koenen. The
smoother or less conspicuously tuberculate forma here included appear to bs genetically
connected with ShosJoceros n. gen. Hamiticeras may also include some of the
tuberculate forma provisionally placed by W, S. Adkins (1628, p. 207-210) under
"ffomiiia." Another form described by Gayle Scott (1988, p. 116, pi, 19, figs. 10, 13)
may also find a place in Hamiliceras,