LEPIDOTUS. 37 



with slightly acuiniiiate crown when unworn ; marginal teeth also stout, smooth 

 and acuminate. Maximum width of operculum nearly two-thirds as great as its 

 depth, and equalling about one-third the length of the head. Ring-vertebrse present 

 in the adulL Fin-fulcra very large ; pelvic fins much smaller than the pectorals 

 and inserted nearer to the latter than to the anal fin ; dorsal and anal fins almost 

 equally elevated, with about fourteen and ten rays respectively, and the former fin 

 with four or five fulcra directly inserted in the back ; anal fin arising opposite 

 hinder end of dorsal. Scales smooth, but showing coarse oblique corrugations 

 when abraded, and those on the flank more or less finely serrated ; principal 

 flank-scales somewhat deeper than broad, those of the lateral line notched ; dorsal 

 ridge-scales acuminate, but usually inconspicuous. 



Description of Specimens. — The type specimen of Lepldotiis mantelll is the 

 hinder portion of the head, with a fragment of the abdominal region and the base 

 of a pectoral fin (PI. VIII, fig. 1), in the Mantell Collection. The type specimen of 

 the so-called L. fittoiii is a vertically crushed and much abraded head, with part 

 of the abdominal region (PI. VIII, figs. 2, 2 a, 2 /;). There are notable differences 

 between these tw^o fossils, as already pointed out by Agassiz ; but the large collec- 

 tion in the British Museum seems to show that these differences are due partly to 

 crushing, partly to abrasion, and partly to great variation in one and the same 

 species. The earliest form is represented by a small specimen from the Purbeck 

 Beds of Netherfield, Sussex, in the Hastings Museum (PI. X, fig. 3). 



The general shape and proportions of the fish are best shown in a specimen 

 discovered by Mr. Charles DaAvson in the Wadhurst Clay near Hastings (PI. VII, 

 fig. 7). This fossil is almost uncrushed, only slightly bent sideways at the base of 

 the caudal fin, and the gently arched contour of the back is especially well 

 displayed. The maximum depth of the trunk is somewhat less than a third of the 

 total length of the fish, while the head must have occupied nearly a quarter of the 

 same length. The greater part of the caudal fin is, of course, missing in this 

 specimen. 



The chondrocranium is well ossified, the various elements appearing in the 

 fossil as pieces of thick, spongy bone. No supraoccipital has been observed, but 

 its ordinary place in the occiput is occupied by the inner part of the large epiotics 

 which meet in the middle line (PI. X, fig. 1, cjw.). These bones, which have a 

 triangular posterior face, form about half the depth of the occiput and rest directly 

 on the exoccipitals (exo.), which also meet in the middle line above the foramen 

 magnum [f.m.). In the fossil shown in PI. X, figs. 1, ] a, the exoccipitals are 

 slightly crushed above, so that the epiotics form an overhanging ledge, but the 

 general shape of the bones is well indicated. Each exoccipital ends postero- 

 inferiorly in an occipital condyle, and its concave posterior face slopes upwards 

 and forwards, separated by a sharp angulation from its lateral face, which is 

 extensive, since the bone enters for a considerable distance into the lateral wall of 



