32 H. Doc. 129. 



Prionodon of Miiller and Henle. The larger and broader ones having 

 the edges serrated, especially near the base, while the narrower ones 

 are smooth and sharp. These differences correspond exactly to the 

 differences observed by Miiller and Henle between the teeth of the 

 upper and lower jaw in some 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 dis- 

 tinguish from Sphyrna by the difference in the shape and serrature of 

 the teeth in the upper and lower jaw The species may be designated 

 under the name of Prionodon antiquus. 



My Galeocerdo denticulatis, 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 dis- 

 tinctly out from its base as in true Galeocerdo. 



HEMIPRISTIS, Agass. 



5. H. HETEROPLEURUS, Agass. The genus Hemipristis was estab- 

 lished 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, Cali- 

 fornia. 



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 Hemipristis of the west from 

 those of Europe. It would seem extraordinary, however, to find the 

 same species of sharks extending from the Pacific coast of this conti- 

 nent to central Europe, especially when we find, upon closer examina- 

 tion, our living sharks more closely circumscribed within narrow lim- 

 its than was formerly supposed. And yet all the differences I per- 

 ceive between the Hemipristis of California and those of Europe con- 

 sist in a marked inequality between the serrature of the hinder margin 

 when compared with that of the anterior margin of the tooth. 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 con- 

 stant or not. 



CARCHARODON, Smith. 



6. c. R.ECTUS, Agass. Of all the types of sharks' teeth that of Car- 

 charodon, next to Lamna and Oxyrhina, is the most numerous in the 

 tertiary deposits, though there is only one living species known. 



