18 FOSSIL FISHES OF THE ENGLISH CHALK. 



plate, imperfectly preserved in the original of PI. Ill, fig. 1 {snhv. 2), is quadrangular, 

 almost twice as long as deep, and marked on its outer face by rows of coarse 

 tubercles and rugge, whicli are mainly disposed in an antero-posterior direction. 

 Its antero- superior angle is produced forwards into a sharply pointed stylet above 

 the very small, triangular anterior supramaxilla {sin,r. 1), which is similarly orna- 

 mented. The mandible is deep, especially in the coronoid region, and the lower 

 half of its outer face, immediately alcove the tuberculated lower edge, is impressed 

 with a deep, continuous fossa for the slime-canal. Above this fossa the longitudinal 

 inedian ridge is coarsely tuberculated, especially where it expands a little on the 

 angidar bone (ar/.) and exhibits a disposition of the tubercles in oblique rows 

 directed downwards and backwards. Above this ridge the bone is again smooth, 

 and the widened, overhanging edge of the dentary (//.) bears a band of minute, 

 blunt teeth like those of the premaxilla. 



The deep and large hyoid arch, seen from the inner side in PI. VII, fig. 1 

 (partly shown also in PI. Ill, fig. 1), is suspended from the lower end of the hyo- 

 ]nandibular {Inn.) by a long and slender stylohyal or interhyal (///.). The triangular 

 epihyal {eph.) is relatively small ; and the large ceratohyal {cli.) has a broad plate 

 of bone connecting the two upper extremities of the ordinary hour-glass-shaped 

 element. The short and deep hypohyal {hij.) is subdivided into two pieces by a 

 transverse suture, the larger piece being below. Fragmentary remains of a large, 

 thin, laminar urohyal are also ol)servable in several specimens. The whole arch is 

 indeed closely similar to that of Beryx. 



The greater part of the cheek is covered l)y the ring of circumorbital plates 

 (PL III, fig. 1, CO.), whicli are small and narrow behind the eye but much extended 

 lielow. Their orbittil margin is everted and tubercidated, while their lower margin, 

 immediately above the maxilla, is clearly serrated ; but the middle portion of all 

 the plates is quite smooth and forms a deep channel for the reception of the slime- 

 apparatus. The shape of the relatively large anterior circumorbital is well shown 

 in PL III, fig. 1 (fto.) ; and it appears to have been articulated with the prefrontal. 

 Scales are very rarely seen. on the cheek behind the circumorbital ring, but they 

 seem to have been present (B. M. no. 258G3). 



The opercular apparatus is complete, and satisfactorily observed both in PL III, 

 fig. 1, and in a specimen described and figured in the ' Catal. Foss. Fishes Brit. 

 Mus.,' pt. iv, p. 400, pi. xvi, fig. 4. The preoperculum {pop.) tapers to the upper 

 end of the hyomandibular and gradually curves forwards at its lower end, without 

 much expansion of the rounded angle. It is deeply grooved for the slime-canal, 

 and the two thin edges of the bone bounding this fossa are delicately serrated. 

 The operculum {op.) is nnich deeper than wide, and its hinder border is produced 

 into two short and broad spines, of whicli the ujjper is connected by a strong ridge 

 Avitli the point of suspension. Its outer face is marked Avith a tul)ercular and 

 rugose ornament radiating from the same point. The subopercuhim, almost want- 



