MOSASAURUS. 57 



presents its inner and outer surfaces separated by minutely denticulated ridges, and 

 subdivided, though less distinctly, into narrow planes. The length of the crown is 

 twenty-two lines ; -its antero-posterior diameter at base eleven lines ; its transverse 

 diameter twelve lines ; its inner circumference twenty-eight lines ; and its outer 

 circumference eleven lines. The inner surface is obscurely subdi- 

 vided into nine or ten planes, disappearing towards the apex of the 

 crown ; the outer surface into three or four planes, equally obscure, 

 and disappearing in the same manner. The accompanying out- 

 lines, No. 5, represent sections at the base and near the apex of 

 the crown. 



The fang is moderately curved, cylindroid, and measures about 

 two inches and a half in length, of which the extra-alveolar portion 

 comprises about half an inch. The bottom presents an elliptical funnel-shaped pit 

 narrowing into the canal of communication with the pulp cavity. The sides of 

 the fang exhibit no trace of excavations corresponding with cavities for succes- 

 sional teeth. 



8. A tooth, from Monmouth County, New Jersey, presented to the Academy of 

 Natural Sciences by Dr. J. H. Slack. The specimen, represented in Fig. 2, Plate 

 IX, resembles that last described so nearly that it looks as if it might have been 

 derived from the same individual, though it is considerably smaller. 



The crown is seventeen lines long, with the base eight lines in diameter antero- 

 posteriorly and seven lines and a half transversely. The surfaces of 

 the crown are less unequally divided than in the preceding specimen ■'^°" ^' 



by the usual ridges, which in this case are rather obscurely denticu- 

 lated. The outer surface of the crown is subdivided into four planes, 

 merging into three and disappearing towards the apex; the inner 

 surface is subdivided into eight planes, likewise becoming obsolete 

 towards the apex. The accompanying outlines. No. 6, represent transverse sections 

 of the crown from near the base and apex. 



The fang is twenty-three lines long, and closely resembles that of the preceding 

 specimen, in its form, the entrance to the pulp cavity, and in the absence of an 

 excavation produced by a successional tooth. 



9. A mutilated tooth, which accompanied the latter specimen, from the same 

 locality and donor. It is larger and has a proportionately shorter and more robust 

 fang than the preceding. The crown is more equally divided by 



the usual ridges, and the surfaces are more distinctly subdivided 

 into planes ; the outer surface exhibiting five, the inner surface 

 nine. These indistinctly multiply near the base of the crown, 

 and diminish in number and finally become obsolete towards the 

 apex. The antero-posterior diameter of the base of the crown is 

 eleven lines ; the transverse diameter nine hnes. The accompany- 

 ing outline. No. 7, represents a transverse section near the base of 

 the crown. 



The fang is compressed from without inwardly, and measures two inches in 

 length ; sixteen lines antero-posteriorly, and twelve lines transversely. It presents 



8 April, 1865. 



