1857.] OWEN DICHODON CUSPIDATUS. 191 



Section*, which he regards as the equivalent of the Hordwell beds 

 from which Mr. Pytts Falconer obtained the original fossils described 

 by me. 



The present additional fossil, figs. 1, 2, & 3, PI. III., is noticed 

 by Dr. Wright in his excellent '* Contributions to the Palaeontology 

 of the Isle of Wightf;" but, with his accustomed liberality, the 

 discoverer of this rare specimen remitted the full description and 

 illustration of it to me. 



The first and second molars correspond precisely, in both size and 

 shape, with those of the lower jaw from Hordwell described and figured 

 in Geol. Quart. Journ. vol. iv. p. 36. pi. 4. fig. 2, m 1, m 2. 



The crown of each consists of four three-sided cones, in two trans- 

 verse pairs, the inner cones being rather higher, more compressed, 

 and sharper than the outer ones, and almost lanceolate in form. The 

 inner side of the outer cones is smooth and nearly flat ; that of the 

 inner cones, fig. 2, is sinuous, convex in the middle, concave before 

 and behind, with each angle of the base produced into a small ear- 

 like cusp : the ridge from the hind angle of the base of the hinder 

 and outer lobe terminates by expanding into a small cusp behind the 

 base of the hinder and inner lobe, so that there are five basal cusps, 

 besides the two lanceolate lobes, on the inner side of the crown of 

 both the first and the second true molars. The other two sides of 

 the cones meet at an open angle in the two inner cones, and at an 

 acute angle in the two outer ones : the angles are rounded off where 

 they meet, so that the outer part of each lobe, fig. 1, is convex, 

 smooth, and polished. 



Were the summits of the four cones to be ground down to a flat 

 surface, there would result, from the form above described, two pairs 

 of crescentic tracts of enamel, with their convexity turned outwards, 

 as in the Ruminants. And this abrasion has indeed in some degree 

 affected the first molar, wz 1, PI. III. fig. 3 ; the resulting crescentic 

 islands, however, instead of being on a flat surface, are bowed, rising 

 in the middle to the apex of each cone, which is hardly more worn 

 than the part which slopes away from it on each side, along the line 

 where the flat, or sinuous, inner side meets the other two sides of the 

 three-sided cone. The crown of the second molar, m 2, is less abraded : 

 that of the third molar, m 3, has lost only a strip of enamel from the 

 ridges of the anterior pair of cones. 



This tooth, agreeably with the artiodactyle type of m 3, has an 

 additional pair of lobes, fig. 3, m 3, ff. They are smaller than the 

 normal ones : the inner surface of the inner lobe has an accessory 

 cusp at the back part of its base, but not at the fore part. The fore- 

 and-aft diameter of this tooth is 9 lines ; that of the three molar teeth 

 being 1 inch 9 lines. 



The specimens described in the * Quarterly Journal of the Geological 

 Society,'vol.iv. 1847, demonstrated the typical character of the dental 



* " Geology of the North-west coast of the Isle of Wight," Annals and Mag. 

 Nat. Hist., ser. 2. vol. vii. p. 433. 

 t lb. (August 1852). 



