LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 225
BELEUNITLDAE de Blalnvilkt
Acrafeu^is Stolley 1911
Aeroleuthig imprw (Gabb)
(Plal* fl. faun S; Plata S3, 6jor® 1. la, lb)
BelemniUa impressus GABB, Paleont. Calif., vol, 1,1864, p. 68. pi. 0, figs. 2, 2a; North
fork of Cottonwood Creek, Shaata County; vol. 2, 1889, pp. li», 209; "Shaata
group"—STAJJTOJJ, U. S. Geol. Surv., Bull. 133, 189B, p. 8i (in part, pL 20,
figs. 1, 2, 5).
AcroleuUiit TMPRWIO (Gabb) STOLUIT, Foss. Catal., 1920, p. 207.
The holotype of this Bpecica ia in the Museum of Paleontology, University of California,
and haa been carefully studied and compared with many forms from the
Shasta series in California. Tho holotype has a total length of 172 mm. and a maximum
normal diameter of 25 mm.; it ia nearly circular in section but at the upper end
has been crushed and flattened, giving it the appearance of having a flare, aa la shown
in Gabb's figure. This Sare is obviously dus almost entirely to crushing and ia
accordingly negligible. On the side figured by Gabb thia is almost covered by a thin
layer of the prolonged guard, but on the opposite side the wholly septate wall of
the phragnwcono is exposed, protruding from the upper end of the rostrum about 45
mm. on this side. Critical measurements of the holotype necessitate some emendment
of ita description. The actual dimensions of the rostrum, below the point at
which the "flare" begins, are as follows: total length, 127 Run..; maximum diameter,
25 mm. Gabb'a figure of the holotype does not conform to the facts and makes the
form appear much more slender. The apical angle of the phragmacone cannot be
determined from the holotype but, as found in other examples and as indicated in the
figure of the plaaiotype, i t extends through about one-fifth of the guard, and the angle
is about 26 degrees. There iB no evidence in any of the examples studied that the
axis of the phragmacone, or of the guard, is excentric; on the contrary, it is normally
central to tbe guard. The figured plesiotype (Calif. Acad. Set. type Coll.) was
found with others of the same species in the Mitchell zone in the lower part of the
Horsetown group, at Locality 134? (Calif. Acad. S«i.)r on Mitchell Creek, about &
miles south of Ono, Shaata County. It occurs in the same sons on the North fork
of Cottonwood Creek and in other places and ia usually associated with Shaslicrioceras
ptmitnU or with soma form of Ancylocerae, indicating that its horizon
is a little lower than Aptian. It has also been found below tho Mitchell zone. It
has been reported from near Wilbur Springs, Colusa County, in strata of probable
Paskenta age. Gabb'a reference to its occurrence near Mount Diablo, associated
with AuceUa piochi, is probably due to mistaken identity. It docs not seem to have
been found at any place ia the Knoxville series (Tithonian) in either California or
Oregon.
Acrcleuiiits abori^inalii Anderson, n. sp.
CPUto so, firm 1)
The guard of this species is the largest yet described from the Cretaceous of California.
The guard of tbe holotype (Calif. Acad. Sci. type Coll,) has a length of
nearly 7 inches (175 mm.) and a width of 30 mm. The ventral aide is marked by a
broad shallow groove extending from near the apex along the lower one-third of the
guard; guard tapering from near the middle, rounded on tbe back; section nearly
circular; section of phragmacone circular, concentric to the surface, axis nearly
central. This species is not uncommon in the Barr tone near the middle of the