MONOGRAPH 



ON 



THE FOSSIL EEPTILIA 



OF THE 



KIMMEllIDGE CLAY. 



Pliosauris grandis. 



PlesiosaurTjS grandjs, Owen. 'Report on British Fossil Reptiles,' 8vo. 1839, p. 83. 

 Pliosatjrds — Owen. Ibid., 1810, p. 54. 



Tooth. Tab. VII. 



Although abundant evidence of the huge dimensions of the present species of 

 short-necked Sauropterygian has reached me since its first indication from the 

 fragmentary evidence described in my 'Reports' of 1839 and 1840, no specimen 

 has more strongly impressed me with the bulk and power of the old tyrant of the 

 upper Oolitic seas, or, indeed, had exemplified its size on such a scale, as the portion 

 of tooth from Kimmeridge Clay, near Oxford, figured in Tab. VII. This unique 

 specimen forms part of the Palaeontological collection of the Hon. Robert Marsham, 

 to whom I am indebted for the present opportunity of describing it. 



The circumference of the base of the crown measures 7 inches 6 lines, equalling 

 that of a large-sized tooth of a Cachalot (Physetcr macrocephalus). Of the 

 enamelled crown 3 inches are preserved, and about as much of the cement-covered 

 base, the largest diameter of which is 2 inches G lines ; that of the fractured end 

 of the crown is 1 inch 3 lines. The length of the entire tooth may be estimated 

 at between 9 and 10 inches. 



The fractured part of the base exposes a pnlp-cavity (figs. 3, 5) of about 

 2 inches in diameter, with a hard dentinal wall of from 4 to 6 lines in thickness ; 

 the tooth would seem, therefore, to be one that had been but recently protruded. 

 The fractured part of the crown exposes a solid and compact mass of dentine. 

 The generic characters of the tooth stand boldly out, and the crown is subtrihedral, 

 with the two inner or concave sides continued into each other by an uninterrupted 

 curve, and the angles between these facets and the outer or convex side of the 

 tooth being blunted, or rounded off. The terms concave and convex refer to the 

 longitudinal direction ; all the sides are convex transversely, the outer one being 

 the least so. This facet (fig. 1) is further distinguished by the finely wrinkled 

 and unridged surface of the enamel. The wrinkling is produced by short, obtuse, 

 wavy risings, frequently joining, or reticulate, and rather affecting the longitudinal 

 course. The same character is presented by the enamel covering the contiguous 

 parts of the other sides of the tooth, and extends furthest in that represented in 



