24 FOSSIL FISHES OF THE ENGLISH CHALK. 



and ornamentation of the l)ones. The middle portion of the premaxilla (figs. 1, la, 

 pruv.) is less elevated into ajprominence than in the latter species.. The posterior 

 supramaxilla (fig. 1 a, smx. 2) is abont three times as long as deep ; while its orna- 

 ment of longitudinal rugse and tubercles is continued over the outer face of the 

 maxilla {mx.). The mandible exhibits its usual ornamented i-idge ; but the orna- 

 ment consists of very large tubercles, which extend over a series of l^ridges span- 

 ning the longitudinal slime-canal to the loAver border of the jaw. The mandibular 

 slime-canal thus appears as if it were subdivided into a series of pits (fig. 3). 



There are six liranchiostegal rays attached to the right ceratohyal of the type 

 specimen. 



The circumorliital cheek-plates exhil)it their usual development (fig. 1 a, co.) ; 

 ]3ut the everted rim of the lower circumorbital (ao.) which is coarsely tuberculated, 

 is notably wide. The inferior margin of this circumorbital bears oblique pectina- 

 tions. The postero-inferior jjart of the cheek is covered with small scales (.s-.), which 

 are thickened by a few coarse jDectinations and tubercles at their hinder border. 



The opercular apparatus is more coarsely ornamented than in H. Jetresiensis, 

 and the hinder border of the operculum (fig. 2, op.) is curiously excavated 

 immediately above its large spine. Between the main ridges of the ornamentation 

 there are also very fine vermiculating ridges, of which those on the operculum are 

 chiefly directed downwards and backwards. 



The anterior part of the vertebral column is partly shown ])y a specimen in the 

 Mantell Collection (no. -4-004), which is figured by Agassiz, torn, cif., pi. xiv d, 

 fig. 2. This fossil clearly Ijelongs to H. siimis, although the head is very fragmen- 

 tary and most of the ornamented face of the outer bones is destroyed. The verte- 

 brae exposed resemble those of H. leivesiensis, but the four anterior caudal centra 

 are perhaps a little shorter and deeper than in the latter s]iecies. 



The fins are only known by unsatisfactory fragments ; but one specimen (B. M. 

 no. P. 887) seems to show that the pelvic, dorsal, and anal fins were situated as in 

 H. lewesiensis, while there were six ribbed dorsal spines. The same specimen 

 shows part of the squamation. The scales are smaller than usual in the genus, and 

 there were probably about twenty in each transverse series on the flank of the 

 abdominal region. The lateral line (PI. VIII, fig. 4, /.) forms a very prominent 

 smooth ridge on each scale of about the fourteenth longitudinal row al)Ove the 

 ventral border. The hinder margin of the scales is usually destroyed, but when 

 well preserved it bears a few short, coarse pectinations. 



Horizons and Localities. — Probably zone of Hola.^ter snhglohosns : neighbourhood 

 of Burham, Kent ; Dorking, Surrey ; Clayton, Sussex. Probably a Turonian 

 zone : Lewes, Sussex. One specimen in the Bi-ighton Museum (Willett (Collection 

 no. 03) is labellcMl "T'pper Chalk, lirighton." 



