LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 125
University of California. Stewart gives tbe following measurements: length (incomplete),
22 mm.; height (incomplete), IS mm.; thickness of (left) valve, c». 10
mm,; No. 31 450, Stewart also gives a photographic figure of another example,
said to be congeneric with the holotype. The locality of discovery is not definitely
given by Gabb. If Gabb's drawing is mode from the "lectotype" it is somewhat
defective, as stated by Stewart.
Tbe anterior end ia broadly rounded, although having an oblique truncation below
the middle of the forward end; the posterior end is not rounded, as in Gabb'a figure,
but also shows truncation; shell probably gaping at both ends; beaks strongly
incurved, the apex being sub-central, a little nearer the anterior end; shell marked
by a deep umbcnal groove extending from the apex downward and backward to the
basal border, seen distinctly on the outer surface of the shell; behind this and diverging
slightly from it, there is an internal rib, not seen on the surface; both groove and
rib are deeply impressed in the cast of the shell, and between them there is a flat,
tabular rib, as seen on the cast, extending from the apex to the base of the shell.
This species is also the genotype. It is distinctly a wood-borer, and is usually
found in blocks of fossil wood buried in shales. The exact horizon of the holotype
is not known, but & number of good examples of the speciee were found by the writer
in a block of fossil wood, in the shales of the Bradley none on the North fork of
Cottonwood Creek; the largest had a length of 26 ram. The tubes and shelle of woodboring
mollusks, including Ttirnva pltnua Oabb, are found in nearly all parts of the
Horsetown group in the Cottonwood district, but they are particularly abundant
in its upper part, where many fragments of fossil wood also occur. Such shells are
found only in fossil wood.
Tumus ffregariua Anderson, n. sp.
(Pl»w I, 5jnr»7)
The shell of this species approaches the outward form of the preceding, but it is
much smaller and relatively not so high as compared to its length, and it ia more
delicately sculptured than the genotype. The tubes are often found closely crowded
together in blocks of fossil wood, the borings being transverse to the axis of tbe
wood. In one such block 4 incheB square, found in the Neptune zone, more than 400
distinct and nearly parallel tubes were estimated, the usual diameter being 5 to 7
mm. Tho tubes were formed of calcareous shell matter filled with very fine sediment,
their usual length being 60 to 80 mm. At their interior terminations was a zone of
shell and shell fragments. This and many other wood fragments are in the Museum
of the California Academy of Sciences. Although many of the shells are partly
exposed, none of them are sufficiently well preserved and exposed for satisfactory
illustration. For this reason the figure here given is necessarily a composite, although
made from a single colony of shells.
SCAPHOPQDA
DENTALHPAE Gray
Den fait am Linnaeus
Dentalium caUfornic-um Stanton
DtntflKum californicum STA.VTON', IT. S- Geol. Surv., Bull. 133, 1855, p. 02, pi. 12,
fig. 3; Shelton's ranch, 5 mileB north of Paskenta, western Tehama County.
"Shell slender, rather strongly curved; aperture and cross section nearly circular;
surface marked by about eight small angular longitudinal coatee, alternating with
an e