HOPLOPTERYX. 21 



in Dixon's figure. Tlie niaxininm depth of tlie ti-unk is shown to be considerably 

 less than the length from the pectoral arch to the base of the caudal fin ; and the 

 origin of the doi-sal and anal fins is seen to be as in H. leircsiensis. The large 

 characteristic scales are nnich abraded, so that they appear pitted and their hinder 

 •pectinations are fainter than they are i)roved to have been by better-preserved 

 specimens. The lateral line clearly passes along the sixth or seventh longitudinal 

 series above the ventral bordei- ; and it is conspicuously marked by small, smooth, 

 triangular eminences chiefly on tiie covered part of the scales traversed. The 

 general form of the fisli in side-view is better shown by another specimen in the 

 British Museum, which is represented of one-half the natural size in PI. IV, fig. 3. 

 The trunk is much laterally compressed as usual ; but, when seen from l^elow 

 (PI. IV, fig. 2), the ventral face of the abdominal region is observed to be flattened 

 as far back as the pelvic fins {pic), whence the ventral border forms an acute ridge 

 to the origin of the anal fin {a.). 



Some of the principal characters of the head are exhibited by the distorted 

 specimen represented in PI. VI. The large triangular depression at the back of 

 the cranium is distinct, and the small, thin crest of the supraoccipital {socc.) rises 

 from its floor. Traces of the small scales investing this region are also seen. The 

 supraorbital flange of the frontal bone {sph.) is conspicuous, though imperfect at 

 the edge ; and the tubercular ornament of the cranial roof seems to have resembled 

 that of II. lewesieasis. The jaws agree precisely with those of the latter species, 

 except that there are some traces of tubercles along the exposed edge of the 

 anterior half of the maxilla {in,v.). Another specimen, on the slab photographed in 

 PI. V, shoAVS that there are minute clustered teeth on the palatines and also on the 

 thickened end of the vomer, as in Beryx. The large lower circumorbital plate in 

 the specimen figured {no.) appears similar to that of //. lewesiensis ; but other 

 examples {e. g., PI. VII, fig. 2) seem to show that, when unbroken, the everted 

 edge of this plate is relatively wider than in the latter species and rather finely 

 tuberculated. On the cheek behind and below the circumorbitals there are small 

 pectinated scales, as indicated by remains of a second fish preserved on the same 

 block of chalk as the specimen figured. The anterior ridge of the preoperculum 

 {jw}).) seems to exhil^it a slightly sharper bend at the angle than in II. Jewesiensis ; 

 and the operculum {op.) is a little wider in proportion to its depth than in the latter 

 species. The sharp indent between the two flat spines of the operculum is also 

 noteworthy. Its ornamentation is more variable than usual in species of 

 EoplopterijA'. Sometimes the discontinuous oblique ridges and tubercles shown in 

 PI. VI become fused into smooth and regular, nearly parallel ridges (as on one 

 operculum in the left lower corner of PI. V). Sometimes there are fine vermicu- 

 lating rugge between the prominent ridges (B. M. no. P. 3982). Seven branchio 

 stegal rays are exhibited by one specimen on the slab represented in the photograph, 

 PI. V, and there raav have been more. 



