354 Mr. A. S. Woodward on the 



twelve years I have searched in vain among English Creta- 

 ceous fish-remains for further evidence on the subject. The 

 time seems therefore to have arrived for describing the scanty- 

 fragments of Plethodus, so far as they are known, in the hope 

 that this or allied genera may soon be more satisfactorily 

 elucidated by some of the collections of Cretaceous fish- 

 remains which are now being made in other parts of the 

 world. 



The type specimen of Plethodus e.vpansus *, now in the 

 Willett Collection, Brighton Museum, is part of the side of 

 a large dental plate probably resembling the original of 

 PI. XIII. fig. 1 in size and shape. The slightly sinuous but 

 generally convex grinding-surface does not exhibit any 

 punctations, and consists of a thin, yellowish, opaque layer 

 covering the thick agglomeration of parallel vertical tubes of 

 dentine, which form the main mass of the plate. There is a 

 base, presumably of bone, beneath this mass, but it seems to 

 be comparatively thin. The lateral border of the plate is 

 somewhat truncated, and it may have borne a few blunt 

 tubercles, but this is not quite certain. 



The specimen thus briefly described was obtained from the 

 Middle Chalk of Mailing, Sussex ; but the dental plate most 

 closely resembling it in the British Museum (PL XIII. fig. 1) 

 is one of a considerable series of more or less abraded examples 

 from the Cambridge Greensand. It is much battered and 

 also scratched by small boring organisms; but it is evidently 

 almost complete. It measures about (MO m. in length by 

 0075 m. in maximum breadth, and is bilaterally symme- 

 trical. The broader end is gently rounded, and three quarters 

 of the length of the plate in this direction rise to a gentle 

 median convexity. The other end tapers to a point, and its 

 oral face is concave. The grinding-surface of the tooth is 

 not punctate ; its truncated lateral border is covered with 

 rather large obtuse tubercles, which are not coated with 

 ganoine or gano-dentine (fig. la). The bony base of the 

 dentai plate is almost completely obscured by matrix, but 

 where its lower face is exposed it exhibits very fine reticular 

 markings, the main lines being longitudinal, the numerous 

 less conspicuous cross-lines being at right angles to these. 

 This reticulation is still more distinct on a fragmentary 

 specimen from the Cambridge Greensand (Brit. Mus. 

 no. 35392). 



* The type species, Dixon, op. cit. p. 366, pi. xxxiii. rig. 2. For the 

 loan of this and other specimens in the Brighton Museum I am indebted 

 to the kindness of Henry Willett, Esq., F.G.S..and Edward Crane, Esq., 

 F.G.S. * U 



