64 FOSSIL FISHES OF THE ENGLISH CHALK. 



facette, and its miter face (fig. 11) lacks the shallow depression characteristic of 

 /,'. lewesiensis. Its postero-superior angle is slightly incomplete. The premaxilla 

 (fig. 9, pmx.) is longer in proportion to its depth than in the latter species, and the 

 r.ul i;iting ridges on its outer face are strongly tuberculated. The comparatively 

 slender form of the mandible is indicated by figs. 9, 10, although in both these 

 specimens the symphysis is wanting. The articnlo-angular (ag.) is exposed along 

 about half the length of the ramus, and its outer face is completely covered with 

 fine tuberculations, which are not fixed on ridges although they sometimes appear 

 to l)o arranged in radiating rows. The dentary (d.) is similarly ornamented, and 

 the teeth of its inner spaced series are both more numerous and relatively smaller 

 than in E. lewesiensis. 



As in the last-mentioned species, the preoperculum (figs. 9, 10, pop.) is slightly 

 expanded at the lower end. The operculum (op.) has a very characteristic shape 

 and ornamentation. Its radiating lines of tubercles are much finer and more 

 numerous than in E. lewesiensis, and the concentric lines of growth of the bone are 

 especially conspicuous. The horizontal ridge on the inner face of the operculum is 

 very stout (B. M. no. P. 541 G). The suboperculum, though imperfect in the originals 

 of figs. 9, 10 (sop.), is evidently at least twice as wide as its maximum depth; and 

 its very fine tubercular ornament tends to range in lines from the upper to the 

 postero-inferior border. 



The trunk of this species is unknown, but an anterior scute of the lateral line is 

 shown from the inner aspect behind the operculum in fig. 10 (s.). This scute is 

 slightly deeper than broad, rhomboidal in shape, deeply cleft behind and pierced 

 in front by the large slime-canal. It closely resembles the scutes of the lateral line 

 in Eurypliolis (Text-fig. 12, p. 56), and is ornamented on the outer face with 

 radiating series of small tubercles. 



Horizons and Localities. — Probably zones of Holaster subglobosus to Terebratulina 

 gracilis: neighbourhood of Lewes, Sussex ; neighbourhood of Burham, Kent. Zone 

 of Holaster subglobosus : Betchworth, Surrey (W. P. D. Stebbing). Undetermined 

 zone : Dover, Kent. 



Family Dekcetidj:. 



A family of Cretaceous fishes apparently related to the surviving Halosauridae 

 (Text-fig. 17, p. 75) and Notacanthidae. Mandibular suspensorium vertical or 

 inclined backwards, and gape of mouth very wide. Teeth small and numerous, 

 conical and slender. Opercular apparatus complete, with few slender branchio- 

 stegal rays, but no gular plate. Ordinary scales small or wanting, but two or 

 more continuous paired series of enlarged scutes along the flank; no median 

 dorsal or ventral scutes. 



