LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

120 loweb cbetaceodb DEPOSITS in california. and oregon
Aslarlt californica Stanton
Antarte California! STAXTON, U. S. Geol. Surv,, Bull, 133, 18S5, p. 67, pi. fl, figs. 19-
21; "upper part of the Knoxville beds," near Stephenson's, Cola fork of Cottonwood
Creek, Tehama County.
Stanton's excellent detailed description of this species needs no special comment
except as to its assignment to the Knoxville aeries. Tbe species is included in a
list of 18 molluscan Species (Stanton, 1895, p. 14), which also contains Aucella crassifollit,
Lima muUilintata, and Acrotiuthit impretsa {Gabb), all of which are characteristic
of the lower part of the Paskenta group of the ShaBta series, it appears,
however, that this species has a greater vertical range than others of this list, since
it has been found in the lower part of the Horsetown group—the Ono zone—at
Locality 1353 {Calif. Acad. Sci.) near the bridge at Ono, Shasta County, By its
position as well aa by its fauna, the type locality of this species must be regarded as
near tbe base o£ the Paskenta group.
A starts traptioidalvi Stanton
AttarU irapezoidalit STANTON, U. 3. Geol. Surv., Bull. 133,1895, p. 57, pi. 8, figs, 17,
18; 3 miles south of Lowry's, Tehama County.
This species baa been adequately described and figured by Stanton, who has also
stated that it has been found at other localities. The locality given for tbe holotype
aa 8 miles south of Lowry's places it well within the limits of the Paskenta group,
and its occurrence near Reiff, Lake County, associated with Pecten corpplczicosta,
Aualla cratsicoUit, and ITurto vtfourmjts supports this conclusion. Like the two
preceding species this one must also be regarded as representing a low position within
the Paskenta group, and a Valanginian horizon.
Opis Defraneo
Opii californica Stanton
OpxD caUforniea STANTON, U. S, Geol. Surv., Bull, 133, 1895, p. 58, pi. 7, figs. 1-7;
near Stephenson's, Cold fork of Cottonwood Creek, Tehama County.
This is the first reoord of the occurrence of Opi'j in the Lower Cretaceous of California,
although others have since been found. Tbe description given by Stanton
is in part aa follows: ' -
"Shell of medium size, with the outline triangular when viewed from the side,
and cordate in Profile; beaks submediau, narrow, prominent, incurved, and approximate;
surface divided by a sharply angular umbonal ridge into two distinct areas,
of which the posterior one is nearly plane and so abruptly deflected that it is scarcely
viatblft from the side view, although it embraces about one-third of the total surface
of the valve; front and ventral margins regularly curved from lunule to the end ot the
umbonal ridge, where it forms an angle of about SO* with the truncated and deflected
posterior end; surface marked by fine lines of growth and more distant, irregular,
concentric furrows; lunule cordate, Urge and very deep, with its border narrowly
rounded;.. . The hinge shows the characteristic structure of the genua, with a
single very large striated triangular tooth in the right valve and two smaller ones
in the left, of which the anterior is fused with the edge of the shell, - '
The rarity of this genua in the Lower Cretaceous of California ia one of its most
striking aspects. Its stratigraphies! position is in the lower part of the Paskenta
group. It is listed by Stanton (1805, p, 14) with 18 apecifioally named forms, including
A ucella crasaicollh and Belemnite* imprenut.