202 DR. GIBBES' MONOGRAPH OF THE 



3. O. PLiCATiLis, Agassiz. Figs. 155, 156, 157. — This is broad, flat and of 

 moderate thickness, resembling somewhat Ox. xiphodon. It is distinguished from all 

 others of this genus, by having folds on the outer face at the base of the enamel, 

 numerous and well marked in the middle of the tooth. There is a broad furrow near 

 the edges, and two others exist next the middle. The root is thick, without lateral 

 branches, the base of the enamel is parallel on both faces to the base of the root. 



Agassiz described this species as always straight, and Ox. retrojlexa as distinct 

 from its oblique form. He now considers the latter as belonging to Ox. xiphodon. 

 Ox. trigonodon he thinks should be referred to this species. 



My specimens are mostly from the Miocene of South Carolina, though I have 

 several from the Eocene. 



4. O. MANTELLii, Agassiz. Fig. 158. — This resembles Ox. hastalis and Ox. 

 xiphodon, but is much thicker and has the root better developed. The outer face is 

 flat, with farrows next the edges on the lo\^'er half, and a depression in the middle at 

 the base of the enamel, the surface is thus undulated. The inner face is regularly 

 arched, the anterior edge is arched and the posterior curved in the specimen figured. 

 The enamel is horizontal at the base, the root thick and distinctly separated into 

 branches. 



The only specimen I have seen is from the Cretaceous of Alabama. 



5. O. CRASSA, Agassiz. Figs. 159, 160. — Is very massive, thicker than any species 

 except that which I will describe as Ox. Desorii. It is curved inwardly, the outer 

 face is elevated and presents faint traces of furrows, which are so developed in Ox. 

 hastalis. It is nearly equilateral, the edges cutting, though thick, the point tends 

 outwardly ; the root is very thick, the base of the enamel angular on the outer, 

 arched on the inner face. 



My specimens are from the Eocene of South Carolina. 



6. O. MiNUTA, Agassiz. Figs. 161 to 164. — This species is quite small. They 

 are sub-cylindrical, with point and edges rather obtuse. They are mostly straight ; 

 the root very thick in proportion to the size of the teeth. 



Numerous in the Eocene of South Carolina. 



7. 0. siLLiMANi, Gibbes. Figs. 165 to 168. — Among twelve specimens from the 

 Eocene of South Carolina, there is much uniformity. The cone is straight or very 

 slightly bowed on the inner edge, equilateral, acutely pointed, both surfaces convex 

 the inner more so. A peculiarity exists in the great breadth of the enamel at the 

 base, which is similar on both aspects. The root is thick, and forms one third of the 

 height of the tooth. I attach to it the name of Professor B. Silliman, the veteran 

 co-labourer in American science.* 



* Ox Desorrii and Ox. SiUimani were described in the Proceedings of September, 1847. 



