PACHYRHIZODUS. 125 



1. Pachyrhizodus basalis, Dixon. Plate XXV, figs. 1, 2. 



1850. Pachyrhizodus basalis, F. Dixon, G-eol. Sussex, p. 374, pi. xxxiv, figs. 9, 10. 

 1901. Pachyrhizodus basalis, A. S. Woodward, Catal. Foss. Fishes B. M., pt. iv, p. 37. 



Type. — Right premaxilla ; British Museum. 



Specific Characters. — The type species, known only by fragments of the upper 

 jaw. Premaxilla somewhat more than twice as long as broad, its small marginal 

 teeth about nine in number and inclined outwards, its large inner teeth with a 

 long and remarkably straight crown, which is not hooked or inclined inwards. 



Description of Specimens. — Of the two fragments figured by Dixon the pre- 

 maxilla alone is characteristic and must be regarded as the type specimen. The 

 so-called " lower jaw " from Steyning is part of a right maxilla, and may belong 

 either to this or to the next species. The right premaxilla (PL XXV, figs. 1, 1 a.) 

 is slightly imperfect both in front and behind, but displays all the essential 

 characters noted in the diagnosis. The outwardly inclined bases of four marginal 

 teeth [in.) are shown, there are three empty sockets, and a fragment of another 

 tooth appears at each end of the series. The anterior inner tooth (/.) is complete, 

 and its expanded base does not quite reach the inner edge of the supporting bone. 

 The posterior inner tooth is represented merely by its shallow socket. Part of 

 another premaxilla in the British Museum (PI. XXV, fig. 2) exhibits the two inner 

 teeth complete and of equal size, with a small additional or replacing tooth behind. 



There is some reason to infer that the shape of the mandible of P. basalis 

 resembles that of P. gardneri, but bears relatively more slender and less incurved 

 teeth. No associated sets of jaAvs or other remains, however, have hitherto been 

 discovered. 



Horizon and Localities. — Probably zone of Holaster subglobosus ; Burham, Kent. 



2. Pachyrhizodus gardneri (Mason). Plate XXV, figs. 3—8; Plate XXVI, fig. 5. 



1837-44. Hypsodon lewesiensis, L. Agassiz, Poiss. Foss., Feuill., p. 104, vol. v, pt. i, p. 99 (in part), 



pi. xxv a, figs. 1, 2, 4; pi. xxv b, figs. 4 — 7. 

 1846. " Reptile or Fish," T. Smith, Lond. G-eol. Journ., p. 21, with woodcut. 

 1869. Acrodontosaurus gardneri, J. W. Mason, Quart. Joui-n. Geol. Soc, vol. xxv, p. 444, pi. xix. 

 1877. Hypsodon lewesiensis, E. T. Newton, Quart. Journ. Geol. Soc, vol. xxxiii, p. 508. 

 1888. Pachyrhizodus gardneri, A. S. Woodward, Proc. Geol. Assoc, vol. x, p. 314. 

 1901. Pachyrhizodus gardneri, A. S. Woodward, Catal. Foss. Fishes B.M., pt. iv, p. 40. 



Type. — Anterior end of dentary probably from zone of Holaster subglobosus ; 

 British Museum. 



Specific Characters. — A large species, the mandible attaining a length of at 



