90 FOSSIL FISHES OF THE ENGLISH CHALK. 



slopes gradually downwards from the straight occipital border to the rostrum. All 

 the exposed bones are smooth. The basicranial axis is clearly straight (PI. XXI, 

 fig. 1, pas.). The occipital and otic regions have not been well observed ; but the 

 supraoccipital, bearing a slight crest, rises into the hinder overlapped margin of 

 the cranial roof, and thus probably separates the parietals as in the existing 

 Clupeidoe. The parietals and squamosals, or perhaps pterotics, enter into the 

 hinder portion of the exposed, cranial roof ; but this is formed chiefly by the large 

 frontal bones (fr.), which are widest behind and gradually taper forwards, without 

 any expansion in the prefrontal (ectethmoid) region. The front als unite with the 

 parietals and. squamosals in a very wavy suture, and are marked with a con- 

 siderable number of small pittings connected with the sensory canal-system. They 

 also exhibit a sharply-marked, rhomboidal depression in the middle between the 

 hinder part of the orbits. The small mesethmoid is truncated in front. The eye is 

 large, and the sclerotic is distinctly ossified (PL XX, fig. 1, scl.). There are also 

 delicate, smooth circumorbital plates, apparently forming a complete cover for the 

 cheek (B. M. no. P. 9053, from Gault). 



The mandibular suspensorium is inclined so far forwards that the small, fan- 

 shaped quadrate (PI. XXI, fig. 1, qu.) is situated immediately below the orbit. 

 The entopterygoid (&rvpt.) has also been observed as a delicate, ovoid lamina of 

 bone ; but nothing more is known of this arcade. The premaxilla is unknown, but 

 must have been very small. The maxilla is especially stout and forms most of the 

 upper border of the mouth. It is imperfect anteriorly in the type specimen figured 

 (PI. XX, fig. 1, mx.), but is better shown in another imperfect head in the British 

 Museum (no. 47302). It is slightly curved upwards in front and is rather deep 

 throughout its length, except quite at the posterior end where it tapers. Its oral 

 border, as seen in the type specimen, bears a single, uniform, close series of minute, 

 blunt teeth ; and immediately above this border the outer face of the bone is finely 

 granulated or rugose. The comparatively delicate single supramaxilla is only 

 represented by a fragment in the type specimen (PI. XX, fig. 1, smx.) ; but its 

 complete form is indicated by B. M. no. 47302, which shows that it is a narrow 

 lenticular plate extending about two-thirds of the length of the maxilla. The 

 mandible is rather short, tapering at either end, and deepest at the posterior limit 

 of the gape of the mouth. The dentary (PI. XX, fig. 1, <1.) bears teeth similar to 

 those of the maxilla, but somewhat larger and apparently more sharply pointed, as 

 shown especially well by a Gault fossil in the British Museum (no. 36170). Its 

 lower margin is continued backwards as a long process beneath the large articulo- 

 angular bone (ag.). 



The opercular bones arc thin and quite smooth. The exact proportions of the 

 operculum and suboperculum are uncertain, but a line crossing this region in the 

 type specimen (PL XX, fig. I, op. } *<>/>.) seems to denote the suture between them, 

 and, ll so, the suboperculum must have been comparatively deep. Part of this 



