ENALIOSAURS. 



277 



coarse as, but more regular than those of the tooth of the Ich. com" 

 munis ; the surface of the crown is smoother and more poUshed, and 

 the longitudinal lines are due to slightly developed angular ridges 

 dividing narrow flattened tracts, like those of a polyhedron. 



I have not observed more than forty-five teeth on each side of 

 the upper, and forty teeth on each side of the lower jaw. The crowns 

 of the teeth are more frequently found to be snapped ofi^ in this than 

 in the smaller species of Ichthyosaurus, a circumstance which is indir 

 cative of the greater force with which they had been used. 



Ich. lonchiodon{\) (PI. 73, fig. 2). — The teeth are more slen^ 

 der in this gigantic species than in the two preceding ones, and they 

 are straighter than in any other species. Their base is cylindrical 

 and regularly fluted ; a smooth boundary divides it from the crown ; 

 this is conical and is traversed by finer and more numerous grooves, 

 which are minutely and irregularly undulated, but converge with a 

 general longitudinal course to the apex of the tooth. The transverse 

 section of the crown is nearly circular ; the crown tapers gradually 

 to its apex, which is nearer the posterior line than the central axis 

 of the tooth. 



Ich. tenuirostris (PI. 73, fig. 5). — The teeth are more slender, 

 in proportion to their length, in this than in any other species ; and 

 they are also more numerous ; their base is cylindrical, and their 

 crown conical, gradually tapering to an acute apex, and slightly 

 recurved : the basal grooves are regular and longitudinal ; the 

 coronal striae are extremely fine. I have found between sixty-five and 

 seventy teeth on each side of the upper jaw ; of these the posterior 

 third part, or about twenty-five of the teeth, are implanted in the 

 slender maxillary bones, the rest being supported by the dispropor- 

 tionately long intermaxillaries. In the lower jaw there are about 

 sixty teeth on each side. The teeth are directed more obliquely back- 

 wards in this than in the preceding species. 



Ich. intermedius (PL 73, fig. I). — Mr. Conybeare (2) thus 

 characterizes this species : — " The upper part of the teeth is much 

 more acutely conical than in the Ich. communis, and the striee leas, 



(1) Xoyxv, spear ; oSag, tooth. 



(2) Loc. cit, p. 108. 



