j EE " 
APPENDIX. 315 
differences correspond exactly to the differences observed by Müller and Henle between the 
same species of the genus Prionodon. A transverse section of the fossil under consideration 
shows, moreover, these teeth to have a central cavity, as in those of the whole tribe of Carcharias, 
There can, therefore, be no doubt that we have here the first instance of a fossil species of the 
type of Carcharias, of the genus Prionodon, which it will be possible under all circumstances to 
distinguish from Sphyrna by the difference in the shape and serrature of the tooth in the upper 
and lower jaw. The species may be designated under the name of Prionodon antiquus. My 
, Galeocerdo denticulatus from Maestricht may, however, belong to this genus. The tooth of this 
species being rather erect, while in Galeocerdo the crown of the tooth is bent backward, and its 
posterior margin is deeply notched. In Prionodon antiquus, as well as in G. denticulatus, the 
crown is but slightly inclined backwards, and though it tapers rapidly to a conical point, that 
point does not stand so distinctly out from its base, as in true Galeocerdo. 
HEMIPRISTIS, Agassiz. 
5. H. HETEROPLEURUS, Agassiz, Pl. I, fig. 14.—The genus Hemipristis was established by me 
from fossil teeth of the middle tertiaries of Europe. Dr. R. W. Gibbes has since indicated their 
existence among the tertiaries of the Atlantic shores of America, and now we owe to Mr. Blake 
the discovery of a tooth of this genus in the deposits of Ocoya creek, California. I have already 
remarked how difficult it is to perceive the difference existing between Galeocerdo adoncus of 
Europe and the species of that genus existing in California. I am still more doubtful about the 
propriety of distinguishing the species of Hemipristis of the west from thoseof Europe. It would 
seem extraordinary, however, to find the same species of sharks extending from the Pacific 
coast of this continent to central Europe, especially when we find upon closer examination our 
living sharks more closely eircumscribed within narrow limits than was formerly supposed. 
And yet all the differences I perceive between the Hemipristis of California and those of Europe. 
consist in a marked irregularity between the serrature of the hinder margin, when compared 
with that of the anterior margin of thetooth. As this may be found to be a constant character, 
I would introduce the western species provisionally under the name of H. heteropleurus, or until 
the discovery of more specimens decides whether this difference in the serrature of the margin of 
the inner sides of the teeth is constant or not. 
CARCHARODON, Smith. 
6. c. RECTUS, Agassiz, Pl. I, figs. 39-41.—Of all the types of sharks’ teeth, that of Carcharodon, 
| next to Lamna and Oxyrhina, is the most numerous in the Tertiary deposits, though there is 
only one living species known. Mr. Blake has brought a finely preserved specimen of a medium 
sized species of this genus from California. Rather smaller than Carcharodon angustidens, the 
tooth has the same form as that species, only that there are no accessary points upon the sides 
of the base. Considering its size, this tooth is remarkable for its thickness; and in that respect 
it reminds me more of Cacharodon angustidens than any other species. The surface is flat, and 
the tooth straight, as in C. angustidens, and to this character the name rectus is intended to 
allude. Several species of this genus have been described by Dr. R. W. Gibbes, as occurring 
in the Tertiary of the Atlantic States. 
OXYRHINA, Agassiz. 
T. 0. PLANA, Agassiz, Pl. I, fig. 29, 30.—Since the teeth of Oxyrhina are known to differ in 
size, só widely as they do, in the different parts of the” jaw, nothing is more difficult than to 
