LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of specie0 223
The composite character of "Htlicaricyltig aequicaatoiu*" Gabb has already been
shown. Nevertheless the name Helicancylua may bo applied to tbe coiled form involved
in his attempted delineation. Merriam supposed that tbe holotype of Heli-
•ancylua was among the materials left at the University of California by tbe old State
Geological Survey. In a list of "type specimens" at the University, prepared by
Merriam in. 1895, is the name "Helicancylus aequitosiatua" Gabb. In the Museum of
Paleontology there is a small ammonoid bearing this label, hfit it has no further
notation. The label was apparently attached to the specimen by Gabb himself and
probably is the specimen referred to by Merriam as the "type," It has a quite
symmetrical coil and two types of ribs, and ia an example of the young stage of .4UJ-
Iraliaras argua nov., described in this memoir. Incidentally, this Is tbe fourth
species that was included by Gabb under the name "Helicancylua aeguicostaiua."
The holotype of Helicancylu* jjabbi nov.—the genotype of Helieaneyha, as here
emended—is in the muBeum of the Academy of Natural Sciences at Philadelphia, as
already stated. As to ita locality and horizon, little can be said at present; it is
thought to have been found on the Cottonwood Creek near Ona, Shasta County,
and to represent an Aptian, or possibly a Barremian, horizon.
BELEMNOIDEA
In tho upper Mesozoic, namely, the Knoxville and the Shasta series in California
and Oregon, fossil remains of no less than 35 species of cephalopoda of the order
Belcmnoidca are recognisable at present, and there are indications that others will
won be added to tho list. Of this number 19 or more ore found in the Knoxville
series, and at least 1G are confined to the Shasta series. In the Knoxville the great
majority of the known spcciea arc referable to either Cylindroleuthis Bayle and
Zeiler, Bclemnopsia Bayle, or to Pachyteuthis Bayle, of which few, if any, survived
into Cretaceous time. As far as known, there is little or no relationship between
any in the Knoxville assemblage and those in the Shasta series. Nor is their stratigraphic
occurrence continuoua. Most of the forms constituting the Knoxville
assemblage appear to be confined to the upper (Tithonian) part of the aeries, and
at its close they quickly and completely disappear, leaving no recognisable descendants.
The earliest faunae referable to the Cretaceous sequence contain no distinct
traces of the Knoxville types, whereas the belemnoids of the Shasta series belong
to distinct genera, for the moat part, such aa characterize tbe early Cretaccous of
other regions (England, western Europe, and Russia). In the Cretaceous assemblage
the following genera, recognised by Stollcy, are fairly well represented, although
not equally:
AcroUulhia Stolley, 10 species Beltrnnoituihit Pierce, 2 spcciea
Aulacotcuihia Stolicy, 2 apecioa Beltmnapsii Bayle, 2 spcciea
Hibolilet Montfort, 1 spcciea
From the generic character of this assemblage, as contrasted with tbat of the
Knoxville series, it is believed that they entered the California province as immigrant
races, following some profound changes in sea and land conditions in western
America and in the Pacific basin, which opened new connections or avenues of
migration. Although their stratigraphical order is not yet fully known, some of the
Cretaceous assemblage seem to be confined to restricted rones. It is perhaps too
early in their study to give the vertical range of many of them, although wc may
note the zones in which they have been found up to the present.
The earliest representatives of the order appear in almost the lowest Cretaceous