LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON
LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON
LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON
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212 <strong>LOWER</strong> CRETACEOtffi <strong>DEPOSITS</strong> IN <strong>CALIFORNIA</strong> <strong>AND</strong> <strong>OREGON</strong><br />
species of Auttraliceraa bear tubercules, at least in their younger stages. Whitebouse<br />
believed that Tropaevm waa achieved by the abrupt cessation of tiiberculation.<br />
The number of species of this genus occurring in the Lower Cretaceous of California<br />
is not known, but fragmentary examples of the genus indicate more than one- Examples<br />
are not rare in the Argonaut zone and appear in strata just above it, but in<br />
all cases they are found in cither Barremian or Aptian strata. The range appears<br />
to be from upper Barremian to lower Gargoaian. Examples of the genua have been<br />
found in the Lower Cretaceous of the Alaskan coast, near Cook Inlet.<br />
Tropaewn percottalum (Gabb)<br />
(Fbt* 71, flpj« 1; plat* 72. Astro t)<br />
Criocerm percoalatus GABH, Paleont- Calif., vol. 1, 1864, P. 17, pi. 16, fig. 26; pi. 17,<br />
fig. 28a; North fork of Cottonwood Creek, Shasta County (not "Aiuylocer&s<br />
percoaUtlua" Gabb, vol. 2, 1869, p. 138, pi. 24, fig. 19, Voy collection).<br />
Gabb's (1864, p. 77, pis. IS, 17) original figures and description of thia species<br />
afford a fair conception of its form and other characters, although tbey are not at<br />
all complete. His account (Gabb, 1889, p. 136a, pi. 24) included under thia name a<br />
quite distinct species and genua. As no later figures and description of either form<br />
have appeared, the earlier figures of "Crioceraa" percoalotua are selected as representing<br />
Gabb's species. The second form included by him is described herein as<br />
Shoeloccroi behemoth n. sp. Tbe present apecies Trepoetin percoatoium (Gabb) is<br />
not uncommon in the Horsetown group in the Cottonwood district and has been<br />
found as far south as Hayward, Alameda County. Good examples have been found<br />
on Hulen Creek, Cottonwood Creek, Alderson Creek, Bee Creek, Mitchell Creek,<br />
Roaring River, and McCarthy Creek, in all cases in nearly the same horizon. In its<br />
general features it is not unlike T. b&twbanki (Sowerby). In form, coBtation, and<br />
suture lines in its younger stages of development, it resembles Australiceraa, aa<br />
suggested by Whitehouse, although it lacks the tuberculate riba belonging to the<br />
latter. In its older stages it develops the thick, heavy ribs to which its name refers,<br />
In mature shells the section of the whorl is aubquadrate, the ribs nearly straight or a<br />
little flexed forward near the periphery in examples below a diameter of 5 inches,<br />
and it tends to divide, either near tbe dorsal border, or in some eases above the middle<br />
of the side; sides are flattened, Bloping toward the periphery. In older stages the<br />
shell of the body-chamber departs a little from the earlier whorls. The largest<br />
example seen has a diameter of 17 inches.<br />
Shaaloeeraa Anderson, n. genua<br />
The genotype of the present group 'IB its leading speeies 3ha*U)cerai californicum<br />
nov. The specimen iB in the Museum of Paleontology, University of California,<br />
and was mentioned by Gabb under tbe name "Ancyloceras percoatatua" as being "in<br />
the cabinet of Mr. Voy, now deposited in the museum of the College of California."<br />
In its final stages the shell of thia genus acquires the general form of Ancyfocerm,<br />
leaving the early coiled stage and forming a straightened or gently curved shaft<br />
which increases rapidly in section, and finally forming a thick crosier having a<br />
narrowed recurved limb. The earlier whorls are sub-elliptical in section, and the<br />
early part of the abaft retains thia form, but with growth it becomes less compressed;<br />
in its body-chamber the shell becomes more inflated, and in the recurved limb it ia<br />
much reduced in diameter and nearly circular in section; the shell here forma a<br />
few strong costal ridges, more prominent on the ventral side. In its younger whorls<br />
(at least in one species), there are costal ridges which arc interrupted on the ventral<br />
border by the development of small bullae which soon disappear with growth.