196 DR. GIBBES' MONOGRAPH OF THE 



very little, though the enamel is lower on the inner surface. The root is thick, and 

 equal in depth to the height of the principal cone. Agassiz has met with no fossil 

 teeth of the upper jaw. He describes several species. 



Genus LAMNA, Cuvier. 



C. L. Bonaparte, and Muller and Henle, include under Lamna four genera — 

 Lamna, Cuvier; Ozyrhina, Agassiz; Carcharodon, Smith; and Selacke, Cuvier — all the 

 characters being drawn from the external form, and no regard being had to the 

 skeleton or teeth. These genera have teeth so dissimilar that they are easily 

 distinguished; but Odontaspis, which is included in another family, has teeth so like 

 Lamna, that when detached they cannot with certainty be distinguished. Agassiz 

 is doubtful about separating them, though there are some fixed differences which 

 will aid in classing species. Teeth of Lamna are flat, and approach in form Otodus, 

 from which they differ in being of less breadth, and having smaller lateral cones. 

 Those of Odontaspis, on the contrary, are more cylindrical, more twisted, and have 

 lateral cones longer and more pointed. The number varies — Odontaspis taurus has 

 Tisually only one on each side, while 0. ferox has two, sometimes three. 



Aorassiz includes under Lamna all straight teeth provided with small lateral 

 denticles, and doubts when the species described seems, to approach nearer to 

 Odontaspis than to Lamna cornuhica. 



When well preserved, there is no difficulty in distinguishing Lamna from 

 Oxyrhina, since the latter have no lateral denticles. The distinction is more difficult 

 with Otodus, as Lamna compressa and Otodus appendiculatus. 



He also includes under Lamna. another type, which he thinks should form a 

 separate genus, Sphenodus. 



1. L. ELEGANS, ^^a55^>. Figs. 96 to 102. — Lanciform, regular and straight; 

 thickness considerable towards the base of the root, but tapering off towards the 

 point. Inner face ornamented with vertical striae, very fine and numerous, very 

 distinct near the enamel, extending above the middle of the cone. This is a 

 distinctive character, which we usually find better preserved in small teeth. 



The lateral denticles are very small points, sometimes absent, the root is thick, 

 with the branches well developed. Outer face plane or a little elevated, inner very 

 convex so that the tooth has almost the appearance of a slender cone cut through the 

 middle, the edges are smooth and cutting. The enamel extends lower on the outei 

 face, the base straight and horizontal, while it is curved on the inner. 



This species is very common in the Eocene. I have fine specimens from 

 Claiborne, Alabama, kindly sent me by C. S. Hale, Esq., of Mobile, from Richmond, 

 Virc^inia, by Professor Wyman, and from Maryland by J. G. Bruff, Esq. In South 

 Carolina they are abundant. 



