FOSSIL SQUALIDjE OF THE UNITED STATES. 193 



very equal, though sometimes more strongly marked on the anterior edge. The root 

 is thick and more than half the depth. The enamel extends much lower on the 

 outer face. 



The specimen figured is the only one I have seen. It was given me by Professor 

 Frost, of Charleston, and was sent to him from Alabama, and I am disposed to think 

 from the company with which it came, that it is from the cretaceous formation. 

 There is another specimen in the Medical College of South Carolina, and I think 

 there are several in the Cabinet of the Academy from the Cretaceous of New Jersey.* 



6. G. coNTORTUs, Gibbes. Figs. 71, 72, 73, 74. — This is an undescribed species, 

 which is very abundant in the Eocene of South Carolina and Miocene of Virginia. 



The cone is longer and more acute with a twist outwardly in its upper third, 

 which is characteristic. The inner face is rounded, while the outer is undulated ; 

 the edges are regularly indented, and on the anterior next the root the dentelures are 

 more developed. The root is very thick and deep. 



Genus HEMIPRISTIS, Agassiz. 



The species included in this genus are somewhat intermediate between 

 Galeocerdo and Carcharodon, but the peculiar distinctive character is in the 

 disposition of the marginal serratures. They extend only a certain distance towards 

 the point, leaving it on both sides entirely smooth. The dentelures are very strongly 

 marked, as much so as in any species of Galeocerdo ; in other respects these teeth 

 resemble them. They are pyramidal, larger at the base, acute at the summit, and 

 more or less curved backwards. The outer side is almost flat, the inner prominent. 

 The enamel is perfectly smooth, and no folds exist even at the base of the crown. 



Agassiz described two species, but has rejected H. paucidens, and preserved 



H. SERRA. P'igs. 75 to 85. — This has the form of a flat pyramid curved 

 backwards, the edges are cutting, and the notches, which are strongly developed, are 

 continued in some nearly to the point, while in others they are few and low down on 

 the lateral edges. They differ in this respect in the two jaws, as is the case in 

 Notidanus and other genera. In the lower jaw they are more conical, higher, more 

 straight at the base, and less curved at the summit. Some are very acutely pointed, 

 so much so as to lead to the belief of there being more than one species. I have, 

 however, a large number, and have traced them in a series of gradual change of size 

 from the broad to the slender forms. 



They are flat outwardly and prominent on the inner face, which in some specimens 

 is compressed laterally at the lower third, so as to be very protuberant, giving them 



* I have lately received several specimens from New Jersey, for which I am indebted to Mr. Samuel P. 

 Wetherill, and Mr. L. J. Germain, of Burlington. 



