190 FOSSIL FTSTIES OF THK ENGLISH CHALK. 



Ti/pe. — Left mandibular dental plate; British Museum. 



Specijlc Characters. — A small species of doubtful generic position, the 

 mandibular plate attaining a length of about 4 cm. Mandibular dental plate 

 much compressed, with a deeply sinuous oral margin, the beak being prominent, 

 and pointed eminences corresponding with the outer tritors ; post-oral margin 

 partly parallel with the symphysial margin ; beak-tritor subdivided into a short 

 series ; anterior outer tritor small and narrow ; posterior outer tritor represented 

 by a marginal series of minute tritors ; median tritor very narrow and insigni- 

 ficant. Vomerine dental plate relatively broad, prominently convex externally. 



Description of Specimens. — The type specimen is a much-broken mandibular 

 dental plate in the Toulmin Smith Collection (PI. XLI, figs. 5-5 r), but exhibits all 

 the essential characters of the species. The beak-tritor (fig. 5 (•) and the posterior 

 outer tritor (fig. 5 a) are clearly subdivided, while the median tritor (fig. 5 a) is 

 remarkably small. The shape of the oral border and beak and the external 

 thickening are better seen in the original of fig. 6. The vomerine dental plate 

 (figs. 7, 7a), found with the last specimen, is less nearly quadrangular than usual 

 in Isrli.ijodns, with some lateral expansion. 



Horizon and Locniitij. — Zone of Holaster subglohosus : Burham, Kent. 



Gevvs ELASMODECTES, Newton. 



EJasmognaihiis, E. T. Newtou {non J. E. Gray, 1867), Chimaeroid Fishes Brit. Cret. Rocks (Mem. 



Geol. Surv., 1878), p. 43. 

 Elasmodedes, A. S. Woodward, Proc. Geol. Assoc, vol. x, 1888, p. 301. 



Generic Characters. — Mandibular dental plate much laterally compressed, with 

 no definite thickening on the outer aspect; its symphysial facette narrow; anterior 

 tritor subdivided into small points; median tritor absent; outer tritors represented 

 by marginal series of small points. [Palatine dental plate insufficiently known.] 

 Vomerine plate apparently as in Ischyodits. Dorsal fin-spine with a sharp anterior 

 keel, rounded sides, and posterior denticles in a single series. 



TyjJe Species. — Elasmodectes willetti, from the English Chalk. 



Bemarhs. — This genus is known only by the type species and by an equally 

 small species from the English Kinmieridge Clay {Elasmodectes secans, A. S. 

 Woodward, Ann. Mag. Nat. Hist, [(i], vol. x, 1892, p. 16, pi. iii, fig. 3). 



1. Elasmodectes willetti, Newton. Plate XXXIX, figs. 4-0; Plate XL, 



figs. 1-3. 



1878. Elasmognathus tdlhtti, E. T. Newton, op. cit., p. 43, pi. xii, figs. 13 — 15. 

 1888. Elasmodectes vl/Jetfi, A. S. Woodward, Proc. Geol. Assoc, vol. x, p. 301. 

 1891. Elasmodectes willetti, A. S. Woodward, Catal. Foss. Fishes B. M., pt. ii, p. 88. 



