LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 137
The figure and description given by Gabb leaves much to be desired. According
to Stewart this species may also include Paladmete hoffmanni (Gabb) and thia view
seems plausible. Both are from the same locality, as given by Gabb. As the North
fork of the Cottonwood Creek crosses the whole of tbe Horsetown group and a considerable
part of the Chico series, the horizon of the species yet remains in doubt.
CEPHALOPODA
The oldest cephalopod stocks known in the Cretaceous sequences in California
and Oregon include both ammonoids and belemnoids, but their origins are yet unknown.
There is little, if any, evidence that they are derived from stocks found in
the underlying Knoxville series, although some of them may later he traced to
such source.
Among ammonoids, farms af Phyllecera*, Lytoccras, BochianHes, and berriaseUida
are found in the lowest group of the Cretaceous deposits, but they can hardly be
shown to have descended from such stocks in the older aeries, although these are near
at hand, contain some similar stocks, and apparently in part are in sequcncial contact
with them. The cephalopod groups in the Knoxville and Shasta aeries are specifically
distinct, although both contain the genera mentioned above.
Forms of Phyllocwm occur in the upper beds of the Knoxville, and in the loweat
beds of the Shaata aeries, but tbey appear to represent differentapecies—one Jurassic
and the other Cretaceous- Furthermore, successive types of Phtjlloceras appear in
the Shasta series at different levels, although not of a single lineage, and none of tham
can be traced to local Tithonian sources, and most of tbem are of short duration.
Forms of Lytoceraa are known in the Tithonian of the Knoxville, and the genus
appears in the earliest beds of the Shasta series. Different types of Lytoceratida
also appear at intervals in the latter series, particularly in the Horsetown group;
none of these can be definitely traced to local sources, and tbeir nearest allies are
found only in distant regions, as southwestern Asia or Europe. It would seem that
"waves" of Lytoceratids (possibly Immigrations) appear at intervals in the Great
Valley embayments, from unknown sources and by undetermined routes.
Bcrriasellids, near to Berricitella catiito (d'Orbigny), occur in the upper part of
the Knoxville, but they have not been found in the lower beds of the Shaata aeries.
The oldest hoplitids of the Shaata series seem referable to Neoconntes or 7Aum»emn««.
Spcciea of Berriasella appear in higher beds of the aeries, but they are not closcly
related to those of the Knoxville, and tbey soon disappear, leaving no known descendants.
This is true also of other generic groups. Forms of Spilieerat are found
in both series.
Among belemnoids there are numerous species, and genera, found in the upper part
•f the Knoxville, and also in the lower beds of the Shaata aeries, but their genetic
relatione are not close. The type BO far found in the two series do not belong to the
same stocks. Species of CylindroUuthis Bayle and Zeilcr are abundant in tbe Tithonian,
but none are known in the later series. On the contrary, various species
referable to AcroUulhu Stolley, to Belemrmpsis Bayle, and to Be^emno/euMts Pearce
are found in tho Shasta series, ranging from Valanginian to Gargaaian, but none
have been found in the Knoxville series.
From these observations there is little cvidenco that the cephalopod faunas of the
Shaata series have descended from local sources, or that their progenitors are to be
found in the Knoxville aeries, although they were near at hand and seemingly in
position to have been the source of Crctaceous stocks. To what causes may we look
for explanation of these striking facts? In the earlier part of this paper poaaibla
sources of cephalopod stocks in remote regions have been suggested, especially for