16 FOSSIL REPTILIA OF THE KIMMERIDGE CLAY. 



fig. 2, and between the more distant longitudinal ridges on the side represented 

 in fig. 3. There are no longitudinal ridges on the convex side (fig. 1). The enamel 

 here, which is a mere film at the base of the crown, slightly increases in thickness 

 towards the apex; its adhesion to the dentine is promoted by numerous fine, 

 wavy, longitudinal, nearly equidistant, linear risings on the surface of the dentine. 



On the side of the tooth fig. 2 the wavy risings of the enamel become larger, 

 more distinct from each other, and more markedly longitudinal, as they recede 

 from the angle dividing it from the convex side. At about an inch distance there 

 is a definite, longitudinal ridge, of an inch in length, followed by other ridges that 

 quickly increase in length as they approach the concave side of the tooth, having 

 pretty regular intervals of about 2 lines. Between these long and well-marked 

 enamel ridges there are other shorter ones proceeding from the base of the enamel, 

 ofvarying lengths. 



On the side of the tooth fig. 3, which transversely is more regularly convex 

 than the side fig. 2, the strong, longitudinal, enamel ridges begin near the angle 

 dividing it from the smoother convex side, at first with interval of about 3 

 lines, the intervening enamel being wrinkled, then with intervals of 1 or 1^ line, 

 the more numerous longitudinal ridges continuing along the inner or longitudinally 

 concave, but transversely very convex, part of the crown of the tooth. Of these 

 more numerous and closely set ridges, probably the alternate ones only would be 

 extended to near the apex of the tooth, a few of the others being shown to 

 terminate at or near the fracture. The longitudinal ridges are strongly and 

 definitely raised from the general surface of the enamel, and preserve their 

 thickness to near their termination. 



The outer longitudinal contour of the tooth («, fig. 2) describes a simple and 

 slight convexity ; the inner one is wavy, passing from the slight concavity at the 

 crown (b) to a corresponding convexity at the junction of the crown and base, 

 and then again becoming very slightly concave. The transverse diameter of the 

 crown is rather less across the convex side (fig. 1) than in the direction at right 

 angles to this, as from a to I, fig. 2. 



An entire crown of the tooth of a Pliosaurus, of the size more commonly met 

 with, is described and figured in my ' Odontography ' (p. 282, pi. 68, fig. 5). 



In the lower jaw of the Pliosaurus from Kimmeridge Clay at Market Raisin, 

 preserved in the Geological Museum at Oxford, there is evidence of thirty-eight 

 teeth in each ramus, which were probably opposed to as many in the upper jaw. 



I estimate the lower jaw of the Pliosaurus, to which the tooth figured in Tab. 

 VII belonged, at about 8 feet in length. 



J. C. Mansel, Esq., of Langthorne, Blandford, Dorsetshire, has favoured me 

 with a photograph of the lower jaw (7 feet in length) of a Pliosaurus in his. 

 museum. I hope to include a description and figure of that specimen in a future 

 monograph. 



