LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 161
(Pictet). The shell is rather large, broadly umbilicate, finely coatate, but tittle
involute; section of whorl semi-elliptical; having about 260 costae to tbe whorl,
arising partly in the umbilical bullae, from which they separate into two or three
thread-like, somewhat sinuous ribs, at first inclining forward, then rising normally
on the side, then slightly backward, and again forward, crossing tbe periphery without
interruption; the major ribs, below the umbilical bullae, inclining forward in the
dorsal zone; between the umbilical bullae, four to eight simple, single costae arising
in the dorsal rone parallel to the others; suture lines not yet known. A row of minute
tubercules are visible on either side of the ventral zone on each second or third rib.
The holotype (Calif. Acad. Sci. type Coll.) was found at Locality 1065 (Calif. Acad.
Sci.) on Duncan Creek, three-quarters of a mile north of the Ono-Beegum road. It
consists of a little less than one-quarter of a whorl; as nearly as can be estimated,
the complete example had the following dimensions: greatest diameter, 147 mm.;
width of umbilicus, S3 mm.; height of whorl, 33 mm.; thickness of whorl, 33 mm.
This example was found in a hard, dark calcareous concretionary block, similar in
character to the overlying beds, and mingled with others In a broeeiated zone,
brought to tbe surface by faulting from possibly lower beds. With it were found the
holotype of jV«ocomi(« rtiMetft nov. and a large fragment of Crioterat iaJum Gabb.
This occurrence seems to represent the lowest fossil-bearing bed yet found in the
Shasta series in the Cottonwood district, although lower beds are exposed farther
to the south.
HOPLITIDAE Hyatt, emend. Spath
In tbe Lower Cretaceous of California and Oregon there are few Hoplitidg as
compared with contemporary deposits in western Europe or in western Argentina.
Forms with sulcata, or even flattened, periphery are not abundant in the Paskenta
group, and they disappear before the close of the Valaugintan, although supposedly
derivative forms appear in the middle part of the Horsetown group. There ore no
known representatives of either Leopoldia or AcontAodt«ct», and few of either Thurmannia
or Sleueroceraa (s. a,). In restricted areas in the middle or upper part of tbe
Paskenta group are found a few berriasellids of various kinds, especially in the district
south of the delta where the fauna ia dominated by heavy-aholled forms of
Aucella. Few hoplitida have been found in the Cottonwood district north of the
delta, as compared to the number at the south; only two examples have been found
in the Cottonwood district, and three species in tho Riddle district in Oregon, all of
which have come from the Paskenta group. Most of them are regarded as either
Berriatelki or tfcocomitca. In all these forms the periphery is rounded, or only
alightly flattened. The ribs are comparatively simple, or but slightly flexed, and,
when divided, the branching occurs high on tho aide of the whorl, as in the berriasellids.
Neoeemilsa is found in the Paskenta group in the districts north and
south of the delta in California, and in the Riddle district in Oregon, in beds of this
group, although not tbe same species,
TJiurirKinmcv has been found both north and south of the delta area in California,
but none in the district about Riddle, nor in any part of the Horsetown group, If
derivatives of any of these types occur in strata later than the Paskenta, they must
be among the Horsetown forma here grouped under Parahoplitidae Spath, but they
do not appear before late Hauterivian time, and then not in great numbers. In the
middle part of the Horsetown group (Aptian) appear Parahoplitaidei Spath, and a
little higher ParaAopfttcs Anthula and Acanthoplites Siniow, The latter genus
continues into the Hulen beds (lower Albian), and with them, possibly belonging
in the same lineage, forms of Chelomeetat and Doucillciccrai.