250 FOSSIL FISHES OF THE ENGLISH CHALK. 



natural size in PI. LIV, fig. 2. Part of a postorbital cheek-plate (po.) is very thin 

 and smooth, marked only by the circumorbital slime-canal and its few radiating 

 branches. The large fan-shaped quadrate (qu.) is exposed beneath, in direct 

 articulation with the mandible. The premaxilla (pni.r.) is small, short, and deep ; 

 and in front end-view its oral thickening seems to bear the broken hollow base of 

 one or perhaps two relatively large inner teeth. The length of the maxilla (mx.) 

 equals about six times its maximum depth ; its oral border is nearly straight, but 

 the hinder half of the bone tapers a little to the rounded end. In the mandible, 

 the articulo-angular is produced into a thick upturned postarticular process, 

 and the outer face is longitudinally ridged. The dentary (d.) exhibits the 

 characteristic smooth longitudinal bulging of the outer face and the thickening of 

 the tapering symphysis. The teeth are comparatively small, with smooth curved 

 crowns, those of the front of the mandible not much larger than those of the 

 premaxilla. The lower end of the preopercumm (pop.) is much expanded 

 and marked by radiating grooves. The interoperculum (iop.) is equally wide, 

 nearly four times as wide as deep, and marked with fine downwardly-directed 

 grooves. The upper branch iostegal rays (J>r.) are comparatively wide, but 

 gradually pass downwards into narrow rays supported by the ceratohyal. 



Two of the anterior vertebral centra are shown to be shorter than dee}), and 

 the scales resemble those of PacJujrJiizodus subulidens. 



This fossil is distinguished from the corresponding part of P. subulidens by the 

 shape of the maxilla and apparently by the relatively smaller size of the 

 mandibular teeth; but it evidently represents a closely allied species. 



Elopine or Albulid. Plate LIV, fig. 3. 



The imperfect ovoid dental plate shown of the natural size in PI. LIV, fig. 3,. 

 appears to belong to the parasphenoid of some Elopine or Albulid fish not 

 hitherto found in the Chalk. The bone, which is of loose texture, is a flat plate, 

 easily distinguished from the vomer of a Pycnodont. Its oral face is irregularly 

 undulating, and is completely covered with stout, bluntly-conical or rounded teeth, 

 which are very variable in size and have no regular arrangement. The teeth are 

 covered with dull ganoine, and most of them are of the blunt shape shown in the 

 enlarged drawing, fig. 3a ; but some, which appear to be unworn, exhibit a 

 minute tubercle or point at the summit of the crown. They are hollow, with a 

 large pulp cavity, and there are no traces of successional teeth. 



A dentition very similar to that of the parasphenoid in the existing Albula, has 

 already been found in the Cenomanian of France (Pisodus foucardi,H. E. Sauvage, 

 Bull. Soc. Sci. Nat. Yonne, vol. xxxiii, pt. ii, 1879, p. 50, pi. i, fig. 2), perhaps also 

 in the Upper Cretaceous of southern Italy (Glossodus hecJieli, 0. Gr. Costa, Atti 

 Accad. Pontan., vol. viii, 18G4, p. 100, pi. ix, figs. 12, 13). The teeth in Albula, 



