LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

DESCRIPTION OF SPECIES 159
found with 10 other examples at Locality 1349 (Calif. Acad. Sci.) in "Zone Mj" on
the Wilcox ranch, £ miles north of Paskenta, Tehama County. It permits of the
following measurements: greatest diameter, SO mm.; width of umbilicus, 12 mm.;
height of whorl, 23 mm.; thickness of whorl, 10 mm.; umbilical ratio, 0.250:1.
The species appears to belong to the group of Dichotomites froffilia (Pavlow, not
Trautschold), said to have coma from bod "D-4" of tho Speeton section, England.
All specimens of this species were found associated with Aucella cratia, A. cromcoflta,
BerriaeeUa sp., and docJktartrtet paakeniaensis nov. The paratype (Calif.
Acad. Sci. type Coll.} has the following dimensions: greatest diameter, 40 mm.;
greatest thickness, IS mm.
The species is named in recognition of the aid given by Mr. A, I. Gregeraen of the
Texas Company, in making the collections, and in the preparation of traverses across
tho Cretaceous sections in western Tehama County.
DickQiomitet burgeri Anderson, », sp.
(Plata 18. fiium 1)
Shell of medium size, discoidal,. compressed, narrowly umbilicate, finely costate;
periphery narrowly rounded; umbilical walls abrupt, smooth or slightly costate;
major ribs arising on the umbilical walls, nearly straight above its borders, inclined
forward, and dividing into four smaller costae at or above the middle of
the sides; costation tending to become weak or obsolete on the body-chamber. The
holotype (Calif. Acad. Sci. type Coll.) has the following dimensions: greatest diameter,
80 mm.; width of umbilicus, 18 mm.; thickness of whorl, 18 mm.; umbilical
ratio, 0.209:1.
This species differs from the preceding in having finer costae and a somewhat compressed
section of whorl, and in its higher point of branching of the ribs. The holotype
was obtained at Locality 1349 (Calif. Acad. Sci.) in "Zone Mi" of the Paskenta
group on thcWilcoxranch, Smileanorth of Paskenta, Tehama County. It was found
with the preceding, and with the same associates. The species is named in recognition
of interest and aid given by Mr. R. W. Burger of the Texas Company in making
traversed across the Shaata series in western Tehama County, and the making of
important fossil collections in these districts.
Dichatomitei Irichotomovt (Stanton)
Olcotlephanui {Polyptyckite*) trichotonuna STANTON, U. S. Geol. Surv., Bull. 133,
1896, p. 78, pi. 10, fig. 1; 2 miles south of Lowry's, "in the uppermost layers
of the Knoxville beds" (upper part of tfie Paskenta group).
As this species seems closely related to the preceding and following forms, it is
placed with them in Dichotomitet Spath. Moat of these forms occur in nearly the
same horizon in the upper part of the PaBkenta group. In the collections of the
California Academy of ScienccB there are numerous examples of thiB genus from the
Wilcox ranch 5 miles north of Paskenta in the zona of Aucella cratsicoiiis and A.
crasta, some of which closely resemble the figure of the present species as illustrated
by Stanton (1805, pi. 16, fig. 1). On tbe Wilcox ranch the zone of this and
the associated forms io near the top of a thick eequencc of beds dominated by rugose,
heavy-shelled apeeica of Auuila, among which A, craairccoUis is somewhat rare.
These beds have a thickness of about 1200 feet, beneath which are plant-bearing beds.
Dicholomitcs arcgonensit Anderson, n. sp.
(Plata 34, IS tun i)
Shell small, discoidal, compressed, anguatumbilicste, sides sloping toward the
periphery, densely costate; primary costae arising on the umbilical border in con-