II.; FOSSIL FISHES OF THE ENGLISH CHALK. 



radiating ridge-ornament. Below and in front of the eye the exact shape of the 

 plates is uncertain, but the antorbital (an.) is longer than deep, tapers in front, 

 and is traversed by a large longitudinal slime-canal, from which branches and 

 ornamental rugae are directed downwards. The sclerotic does not seem to have 

 been ossified. 



The mandibular suspensorium (PI. XXIII, fig. 2) is inclined so far forwards 

 that the articulation of the mandible is beneath the hinder part of the orbit. The 

 upper end of the hyomandibular is straight, apparently with a single long articular 

 facette; its lower end meets the metapterygoid (fig. 4, m/pt.) and is produced 

 posteriorly into a slender connection with the symplectic (sym.). The quadrate 

 (figs. 2, 4, qu.) is triangular, with a robust articular head, and with an upwardly 

 directed process arising from the lower end of its hinder border to clasp the thick, 

 styliform symplectic. The whole of its upper margin is apposed to the thin 

 triangular metapterygoid (mpt.), and its anterior edge is in contact with the 

 downwardly curved hinder end of the ectopterygoid (fig. 4, ecpt.). The ento- 

 pterygoid seems to be thin, relatively large and antero-posteriorly elongated, and in 

 the specimen figured there is evidence of clustered, minute, pointed teeth either on 

 this bone or on a palatine. The premaxilla is imperfectly known, but it is rather 

 small, underlaps the front end of the maxilla, and is provided with clustered 

 minute teeth. The maxilla (fig. 5, mx.) is robust and arched, with a large 

 upwardly directed process at its anterior end and a convex oral margin, which 

 bears clustered minute teeth like those of the premaxilla. Its exposed outer face is 

 ornamented with a coarse rugosity, in which the principal ridges are longitudinal. 

 Its upper portion is overlapped by two large supramaxillaries {mix. 1, 2), of 

 which the hinder is the deeper and sends a narrow process forwards above the 

 upper margin of the anterior plate. These bones are also rugose. The dentary 

 portion of the mandible (fig. 6, d.), which is nearly smooth, is very robust at the 

 symphysis, and bears a cluster of several series of minute teeth, of which the 

 points of attachment are shown in fig. 5 a. The dentary rises in the coronoid 

 region, and its hinder margin is excavated for the reception of the large articulo- 

 angular (fig. 6, ag.). The lower border of the mandible is slightly bent inwards; 

 and just below the angle there extends the sensory canal, opening on the dentary 

 by a series of pores (seen in B. M. nos. 4294 and P. 6456). The main upright 

 portion of the angular bone is smooth, but its lower face is finely ornamented with 

 rugae. 



The bones of the opercular apparatus are stout, but their outer ornamented 

 face is often more or less flaked away in the fossils. The operculum (PI. XXIII, 

 figs. 1, 2, op.) is trapezoidal in shape, about two thirds as broad as deep, and 

 marked with coarse, branched rugae, which radiate from the point of suspension. 

 The suboperculum (sop.), as coarsely ornamented, is almost sickle-shaped and 

 deeply overlapped by the operculum, and bears a large ascending process at its 



