120 WEALDEN AND PURBECK FOSSIL FISHES. 



tively small size is best shown in the original of PI. XXIV, fig. 1, but the bones are 

 so much broken by crushing that their outlines are rather obscured. The relatively 

 large orbit is bounded behind, below, -and in front by the single series of smooth 

 cheek-plates, which are traversed by the usual circumorbital slime-canal. The 

 gape of the mouth is evidently small. The opercular bones, partly seen also in 

 PI. XXIV, fig. 2, are smooth. The large angularly-bent preoperculum is marked 

 only by the groove of the slime-canal. The operculum is about two-thirds as wide 

 as deep, and the suboperculum is relatively small. The interoperculum seems to 

 be triangular in shape and deeper than wide, its apex rising between the lower end 

 of the operculum and the preoperculum. 



Delicate ring-vertebrae and short slender ribs are exposed by the removal of 

 the scales in the specimen labelled by Egerton (B.M. no. P. 1101). 



The bases of about nine very stout rays are seen spread out in the pectoral fin 

 of PI. XXIV, fig. 1 ; and the foremost pectoral ray in fig. 2 bears a regular series 

 of very slender fulcra. The pelvic fins, which are shown in two specimens to 

 arise midway between the pectorals and the anal, also consist of unusually stout 

 rays. The dorsal and anal fins arise directly opposite each other, but are incom- 

 pletely known. 



The scales are clearly all smooth without any posterior serrations. The depth 

 of the deepest flank-scale, above the pelvic fins, slightly exceeds four times its 

 complete width (fig. 2a). The rhombic dorsal and ventral scales are often pro- 

 duced into a sharp point at their postero-inferior angle, and both the dorsal and 

 ventral ridge-scales are sharply pointed behind (figs, la, 2a). Two rows of 

 scales intervene as usual between the principal flank-scales and the dorsal ridge- 

 series, the lower being slightly the deeper ; while five small scales occur below 

 each principal flank-scale as far back as the pelvic fins, the uppermost being 

 traversed by the lateral line. The ventral scales become fewer behind, as already 

 described in P. formosa (p. 117), and the stout ventral ridge-scales are compara- 

 tively small. 



Horizon and Locality. — Middle Purbeck Beds : Swanage, Dorset. 



5. Pleuropholis serrata, Egerton. Text-figure 35c, n. 



1858. Pleuropholis serratus, P. M. G-. Egerton, Figs, and Descripts. Brit. Organic Remains (Mem. 



Geol. Surv.), dec. ix, no. 7, p. 5, pi. vii, figs. 5 — 9. 

 1895. Pleuropholis serrata, A. S. Woodward, Catal. Foss. Fishes, Brit. Mus., pt. iii, p. 487. 



Type. — Imperfect fish ; collection of late Dr. John Lee, Hartwell. 



Specific Characters. — Imperfectly known, but a comparatively stout fish 

 attaining a length of about 10 cm. Head and opercular bones smooth. Scales 

 also smooth, but those of the deepened flank-series with fine oblique serrations on 

 the hinder border. 



