LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

222 lower CbETACEoUB depobits in california. and oregon
Locality 1057 (Calif. Acad. Sci.) near Mitchell Creek, a mile above its mouth. The
horizon was about 250 feet above that of the preceding species. In size., sections
and in the character of its ribbing, this specie* ia intermediate between H. nvuptiut
and H. miVobiiu, and its stratigraphic position is likewise intermediate between
them. It was found in strata containing Atxotmdhis ahoriginalis, Parahopliloidei
cf. eerrosensis, and others believed to represent a lower Aptian horizon.
/fWtcaneyiuj Gabb, emend.
The name Htlxeancijlus has been continued in paleontologies! literature since its
first appearance (Gabb, 180?a, p. 140). It seema to have been regarded as a valid
generic name by many authors, including Hyatt, J. P. Smith, Spath, and others,
and should be retained. Yet an inspection of the figures given by Gabb may well
cause suspicion that they are not all identical, specifically or geaerically. None
of them has been indicated as the genotype, but they may readily be seen to include
three distinct apecies; two of them are congeneric, but are not closely related to the
third. It seems possible, however, to select one of these &3 a genotype, and thus
preserve the euphonious nsjne Hclicancyiue, without otherwise disturbing its acceptance.
But the description given by Gabb so involves the three forms referred to
that it should be emendedaccordingly. Two of the three species more ncarlyrelatcd
are described in another place under the name ffamiitcerat nov. The third form
included in Gabb's delineation of the genus (Gabb, 1869ft, pi. 23, figs. 20, 20a) represents
a helicoid type, but it has no close relationship to the others.
Although this form resembles Hdxcoceras, it ia the only one to which the name
Helicancylu* seema to be applicable, and may be regarded aa the genotype of Heliameyl-us.
This specimen is in the museum of the Academy of Natural Sciences of
Philadelphia and ia the only example of tho genus thus far recognised or recorded
from the Lower Cretaceous of California. It is the coil of an immature shell and
gives only a partial conception of its mature form. Its asymmetry is readily seen,
not only in Gabb's figure, but in the photographs of the specimen here given. Its
manner of coiling ia thus given by Gabb i "Shell commencing with a dextral, open,
defending spiral, aa in Hdieoeeraf, the spiral afterward opening. ..." But his
statement cannot be followed further without caution. The ribs are all of one kind,
arising on, the dorsal wall, where they at first curve backward, then ascend nearly
normal to the dorsal border and cross the ventral zone without interruption; they
are separated by interspaces broader than the ribs; ribs trituberculate, the tubercules
first appearing on the ribs at a diameter of 10 or 12 mm., becoming more prominent
with the growth of the shell; section of whorl broader than high, tha ratio of
width to height being about 7:5.5; dorsal walla etecp, sides and ventral part of the
section rounded, nearly circular; sutures not known. The apparent straightening
of the coil in its later stage perhaps led Gabb to associate it with the forms here
placed in Hamificcras, but their near relationship can hardly be maintained, even
granting that the early stages of tha latter are not yet known. Nor ia the adult stage
of the coil referred to yet known, and it should not be assumed from
the known data. Some further conception of the genua may be gathered from the
description of the only known specics, namely, Helicancylus gabbi nov.
ffcii'eflMcyltts jaiffri Anderson, n. ap.
tFI»n 79, fig 5}
ffelicancytm aequicasialut GABB (in part only), Paleont. Calif,, vol. 2. 1869, p. 141,
pi. 25, FIGS- 20, 20A (not figs. 20, b-G); Cottonwood Creek, Shasta County.