EDAPHODON. 185 



tlie inner aspect; beak-tritor composed of a series of laminte, the other tritors 

 consisting of numerous tubules ; median tritor divided (except when abraded) into 

 two small and widely-separated parts, of which the anterior is placed on the edge 

 of the symphysis, and the posterior behind the anterior outer tritor. Palatine 

 plate with very large tritors, the two inner being broad, and the posterior of these 

 tending to overlap the narrow outer tritor. Vomerine plate with a concave 

 or grooved symphysial surface ; the anterior tritor much larger than the others. 



Description of Specimens. — Though found most abundantly in the Cambridge 

 Greensand, the dental plates of this species appear to occur at all horizons in the 

 Chalk. Only one specimen, however, from the Chalk near Lewes, has hitherto 

 been discovered to show all the dental plates of one mouth in a satisfactory state 

 of preservation. This has already been described and figured by E. T. Newton, 

 loc. cit., whose drawings of the left palatine and left mandibular dental plates are 

 copied in Text-figs. 54, 55. In the mandibular plate the relative prominence of 

 the beak varies considerably in different specimens, and the appearance of the 

 inner or median tritor depends on the extent to which it is uncovered. In 

 the left mandibular plate, shown in PI. XL, figs. 4 — 4 h, for example, the beak 

 is much longer than in the original of Text-fig. 55 ; while its median tritor (e.) is 

 exposed only in two narrow patches and appears to be completely subdivided into 

 two parts. The anterior outer tritor of the same specimen (fig. 4rt, c.) is also 

 relatively small and well separated from the outer oral margin. To the same 

 individual as the mandibular plate belongs the vomerine plate shown in PI. XL, 

 figs. 5 — 5 h. This, again, is remarkable for the prominence of the beak, and 

 suggests that the vomerine dental plates named Edapliodon gigas by Egerton 

 (Quart. Journ. Geol. iSoc, vol. iii, 1847, p. 352, and Newton, oji. cit., p. 17, pi. v, 

 figs. 1, 2) really represent a variety of E. seilgwiclci. Its beak-tritor is relatively 

 large ; the next four tritors are small ; and then the sixth tritor of the series is 

 of considerable size. 



Horizons and Localities. — Senonian zones : Norwich. Turonian zones : neigh- 

 bourhood of Lewes, Sussex. Zone of SchloenbacJna rariaiis : Dover, Kent. Also 

 Gault, Red Chalk, Cambridge Greensand, and Lower Greensand. 



2. Edaphodon mantelli (Buckland). Plate XLI, fig. 1. 



1835-36. Chimxra manfeUii, W. Buckland, Proc. Geol. Soc, vol. ii, p. 206, and Phil. Mag. [3], 



vol. viii, p. 5. 

 1843. Ischyodus mantelli, P. M. G. Egerton, Proc. Geol. Soc, vol. iv, p. 156. 



1843. Chimxra (Psiitacocloti) mantellii, L. Agassiz, Poiss. Foss., vol. iii, p. 348, pi. xln, figs. 1, 2. 

 1847. Edaphodon mantellii, P. M. G. Egerton, Quart. Journ. Geol. Soc, vol. iii, p. 352. 

 1850. Edaphodon mantelli, F. Dixon, Geol. Sussex, p. 203, pi. xxxiv, figs. 6, 7. 

 1878. Edaphodon mantellii, E. T. Newton, Cliimaeroid Fishes Bi-it. Cret. Rocks (Mem. Geol. Surv.), 



p. 14, pi. iv, figs. 1 — 9. 

 1891. Edaphodon mantelli, A. S. Woodward, Catal. Foss. Fishes B. M., pt. ii, p. 75. 



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