LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

DESCRIPTION OF SPECIES 113
common in the Horsetown group. Auceffa craasicollis pertftina to the Paskenta group.
None of tho species have been recorded from the Knoxville (Upper Jurassic) series,
nor have any been found there by the writer. From an analytical study of the list
it must be concluded that the locality must be included in the Paskenta group, and
an examination of the beds shows them to immediately overlie a heavy conglomerate
marking an unconformity at the base of this group.
MYIILIDAB Fleming
Mylihta Linnaeus
Mijiilm arlingloni Henry (unpublished)
(Ptita 1, fifuro A)
Shell of medium size, obliquely crescent-shaped; beaks terminal, narrowly
rounded; cardinal line slightly curved, curve accentuated in the more strongly arched
posterior border; anterior margin slightly concave in young stages of growth, more
strongly concave in older shells; valves strongly arched (inflated), when seen from
the front; dorsal slope bearing a subsidiary fold parallel to the umhonal ridge; teat
thick.
The holotype is in the Museum of Paleontology, University of California, It has
tbe following dimensions: total length, 91 mm.; height, 10 nun.; convexity of single
valve, 18 mm. Another example of the same species was found at the same locality.
These were found by Leonard W. Henry on tho south border of Contra Costa County,
near Arlington Avenue at the north border of Berkeley. They were found associated
with other invertebrates, including ifalunus sp,, Aucella cratrteollti, A, inflala, and
BtlemniU» sp. These fossils were found in a calcareous pebbly sandstone overlying
Kncxville beds with clear evidence of unconformity, as shown in part by some of the
associated forma. The horizon represented is in tbe lower part of the Paskenta
group of the Shasta series.
Modioli Lamarck
.WchJioiu» major (Gabb)
Modivla major GABB, Paleont. Calif., vol. 2, 1809, p. 191, pi, 13, fig. SB; white limestone
of the "Shasta Group,' 11 east of Knoxville, itfapa County-—STANTON,
U. 8. Geol. Surv., Bull, 133, 1806, p. 48 {in part, not pi. 3, fig. 1)-ANMREON,
Calif. Acad. Sci., Pr., vol, 2,1602, p. 46; north border of Berkeley, California;
Paslconta group,
Myoconcha major (Gabb) STJWA&T, Phila. Aead. Sci., Spas. Publ. no, 3, 1330, p. 104,
pi. 4, fig. 1; probable holotype.
Gabb's holotype of this species seems to have been taken to the Academy of
Natural Sciences of Philadelphia, and Stewart has figured an example found there
as probably the holotype. The species occurs in the white limestone lj miles southwest
of Wilbur Springs, Cotuaa County, associated with Khy^ttAonella whi/ncyi Gabb
and Peeltn eomplexieo»la Gabb. An imperfect example of this species is in the
California Academy of Sciences from this locality, and ia readily identified with
Gabb's form. The same species has been obtained from the white limestone of the
same horizon on the weBt side of tho Bcrryessa. Valley, collected by £ldridge D.
Drew and donated to the Academy, The same species occurs in a calcareous sandstone
of tbe Paskenta group in tbe Berkeley Hills near Berkeley. The measurements
of the holotype given by Gabb are; length, 4.8 inches; height, 2,4 inches; thickness,
1.5 inches. The ratio of height to length given by Stewart for the probable holotype
is .480:1, which is somewhat more slender than as stated by Gabb.