EDAPHODON. 187 



anterior and post-oral margins that its shape is not completely shown. A nearly 

 perfect left mandibular dental plate, however, is represented in PL XLI, figs. 2, 

 2 a, 2 h, and exhibits all the characters of the species. Its outer face (fig. 2) is 

 marked only by the usual structural lines, without any supplementary layer near 

 the oral border. The symphysial facette is well marked off from the rest of the 

 inner face (fig. 2 a), and in this well-preserved specimen the median tritor (e.) is 

 exposed only in its upper portion, where it is continuous. The two outer tritors 

 (fig. 2h, c, (L) are small and placed slightly within the oral margin. The upper 

 dental plates remain unknown or unidentified. 



Horizon and Localities. — Zone of Holasfpy stibglohosiis : Hamsey and Southeram, 

 Sussex; Burham, Kent; Dorking, Surrey. 



4. Edaphodon reedi, Newton. Plate XL, fig. G. 



1878. EdapJiodon reedi, E. T. Newton, Cliiuiseroid Fishes Brit. Cret. Eocks (Mem. Geol. Surv.), 

 p. 19, pi. vi. 



Ti/pe. — Mandibular dental plate ; York Museum. 



Specific Characters. — Dental plates with tritors excessively reduced. Man- 

 dibular plate with a very prominent beak, and the symphysial facette occupying 

 at least one-third of the inner aspect; beak-tritor composed of a series of laminae, 

 the other tritors consisting of numerous tubules ; median tritor reduced to a small 

 space on the edge of the symphysis ; posterior outer tritor often absent. Palatine 

 dental plate with the posterior inner tritor very small or absent, and the outer 

 smaller than the anterior inner tritor. 



Description of Specimen. — This is a large species represented by several dental 

 plates from the Cambridge Greensand, but apparently known only by one specimen 

 from the Lower Chalk. Even this fossil (PI. XL, fig. 6) is not very characteristic, 

 and exhibits an extreme reduction of the tritors. The dental plate is evidently 

 incomplete behind, but is otherwise damaged only by a transverse fracture. There 

 is only one diminutive, elongated inner tritor (a,), while the outer tritor (c.) is 

 reduced to insignificance. 



Horizons and Localities. — Zone of Holaster stthglohosns : Gljnide, Sussex. 

 Cambridg-e Greensand. 



'o' 



FiN-SPiNE OF Edaphodon. 



A large part of a dorsal fin-spine is associated with one specimen of the 

 mandibular dentition of liJ. agassizi described by Newton (loc. cit., p. lo, pi. iii, 

 fig. 3). The fin-spine of Edaphodon is thus shown to resemble that of the existing 

 Chinisera and also that of the typically Mesozoic genus Ischyodns. It is long. 



