10 WEALDEN AND PURBECK FOSSIL FISHES. 



laterally just behind the position of the hjoraandibular, and seems to have been 

 fixed on a special cartilaginous support {.v.). It is of the form originally named 

 SpliP)ioiicIiHS, with a trifid inserted base, from which rises a sigmoidally arched 

 enamelled spine, barbed at the apex (fig. 2^t). As observed in B. M. no. P. 11872, 

 the postero-inferior limb of the base is largest and longest and truncated at the end, 

 while its long axis is slightly oblique to that of the other two limbs, "which are 

 nearly in the same line but curved. The exserted spine, which rises as nsual at 

 the place of meeting of the three basal limbs, is at least as long as the postero- 

 inferior linil), laterally compressed, and sufficiently unsymmetrical to show that it 

 is not a median structure. It is completely covered Avith enamel, which is smooth 

 at the barbed apex and along the narrow upper face ; but its basal portion is 

 marked with irregular sharp ridges, which cover the greater part of the antero- 

 lateral face and here terminate abruptly above at a sharp longitudinal ridge which 

 extends to the apex. 



The head and at least the anterior portion of the trunk are covered with a 

 spinous shagreen, which is always fine, 1)ut varies a little in size in different 

 regions. Each tubercle (PI, II, figs. 1 c, 1 d) is hollow, with an expanded trumpet- 

 shaped base, more or less crimped round the edge, and marked with radiating- 

 ridges on its outer face. It rises in the middle into a laterally-compressed recurved 

 booklet, on which the vertical ridges end abruptly at the arched anterior border. 



Horizon, (iml Localiticfi. — Weald Clay: Atherfield, Isle of Wight; Cooden 

 Beach, Pevensey Bay, Sussex. 



Addendum. — Isolated teeth of the same general type as those of H. hasamis also 

 occur in lower horizons of the Wealden series, but are not sufficiently similar to be 

 referred with certainty to this species. Some obtained by Mantell from the 

 Tunbridge Wells Sand of Tilgate Forest seem to have the principal cone less 

 compressed and the inner lateral denticles more slender and acuminate than in 

 H. hasamts (as shown in Catal. Foss. Fishes, Brit. Mus., pt. i, 1889, pi. xi, figs. 14, 

 15). Rolled and water worn fragments of such teeth were named OxyrJiina 

 {Merisfodon) paradoxa or Meristodon paradoxus by Agassiz, Poiss. Foss., vol. iii 

 (1843), p. 286, pi. xxxvi, figs. 53—56. 



Abraded and fragmentary small dorsal fin-spines from the Tunbridge Wells 

 Sand of Tilgate Forest also closely resemble those of H. Jnaoiinis, but can scarcely 

 be described as identical. They were named Hyhodvs svhcKv'uiatns by Agassiz, 

 Poiss. Foss., vol. iii (1837), p. 46, pi. x, figs. 10 — 12; and an early figure of one 

 specimen was given in Trans. Geol. Soc. [2], vol. ii (1820), pi. vi, fig. 0. Two 

 nearly complete fin-spines, less abraded than usual, from the Wadhur'st Clay near 

 Hastings, are shown in PI. Ill, figs. 6, 7, and appear to be essentially identical 

 with those of H. ha^anus, having the same fine longitudinal ridges and small 

 posterior denticles. The Ijroader spine (fig. 6) is a little widened \)j crushing ; 

 the narrower spine (fig. 7) exhibits only the l)roken bases of the posterior denticles. 



