Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

APPENDIX.
SCYMNUS, Cuv.
2. s. OCCIDENTALrS, Agassiz, P1. I, figs. 9-13.-The few species upon which Cuvier founded
the genus Scymnus have been of late subdivided by Muiller and Henle into two genera-Scymnus proper, and Lemargus-all of which are only known among the living. It is another
of the highly interesting discoveries of Mr. Blake to have brought home two teeth from the
Tertiaries of California belonging to this remarkable type. I would even not hesitate to consider
them as indicating a distinct genus, were the number of specimens sufficient to warrant the
inference that the teeth present in every position of mouth as great a difference from the true
Scymnus and Lemargus as the two latter present when compared with one another. At all
events these teeth belong to the genus Scymnus, as established by Cuvier, and constitute a
very distinct species, on account of the strong bend backwards of the main point of the tooth,
and the distinct, and rather marked serration of the edges of the crown. Moreover, the inclination of the central point upon its basis gives these teeth a certain resemblance to those of
Spinax and Centrophorus, and still more with Galeocerdo. The connexion of the teeth of the
same row of the jaw with one another, was evidently the same as in the Scymnus and LTmargus,
as is plainly shown, by the notch upon the inner surface of the root, and the articulating tuberde
at the base of the enamel in both sides. The discovery of a fossil Scymnus in the Tertiaries of
California is particularly interesting in a geographical point of view, since thus far no representative of the type has been found in the Pacific ocean.
GALEOCERDO, hiiller and Henle.
3. G. PRODUCTUS, Agassiz, PI. I, fig. 1-6.-Two species only, of living Galeocerdo have been
known thus far; one from the Indian ocean, and one from the Atlantic. The fossil species
have been traced from the chalk to the upper Tertiaries.
The Atlantic States have already yielded satisfactory indication of the presence of this genus,
during the tertiary period, on the eastern coast of America. Now we receive from the collection
of Mr. Blake a new addition to the range of this remarkable genus. The new species he has
discovered resembles so closely the Galeocerdo adoncus from the Eocene of Europe, and especially
common in the molasse of Switzerland, that were there not several specimens in the collection,
agreeing with one another in every respect, and unitedly differing from those of the Old World,
I would have been at a loss to distinguish them.
The California species differs chiefly from the European in having the anterior margin of the
tooth less arched, with much more minute crenulations, and the serratures on the basilar margin
rather smaller.
PRIONODON, [iiller and Henle.
4. P. ANTIQUUS, Agassiz, P1. I, figs. 15, 16.-Thus far no fossil shark of the tribe of Carcharias
has been known among the fossils; and, as shown in the Poissons Fossiles, all the species formerly
referred to the genus Carcharias have been ascertained to belong to the genus Carcharodon.
Few discoveries in this field could, therefore, be of more interest than finding among the
tertiaries of Ocoya creek a number of teeth agreeing in the deep notch upon the base of the
root, but differing in their width as well as in the shape of their edge; belonging evidently to
the genus Prionodon of Muiiller and Henle. The larger and broader ones having the edges
serrated especially near the base, while the narrow ones are smooth and sharp. These