120 FOSSIL FISHES OF THE ENGLISH CHALK. 



type species. Length of cranium equalling twice its width at the occiput; each 

 parietal bone broader than long; rostral region very narrow and tapering; frontals 

 without rugose ornament on the lateral expansions, only marked by structural 

 lines. Exposed area of scales ornamented with tubercles and reticulating rugae, 

 scarcely radiating. 



Description of Specimens. — The type specimen (PI. XXIV, fig. 1) displays the 

 characteristic skull from above and behind, with parts of the opercula, other 

 scattered bones, and a few anterior vertebra?. The other known specimens 

 exhibit only the head and the anterior part of the abdominal region. 



The shape and contour of the cranial roof are well shown in the type specimen 

 (fig. I). The supraoccipital (sore.) and epiotics (epo.) form a very narrow rim at 

 the occipital border, and the latter bones project as a pair of bluntly-pointed, 

 backward prominences. The parietal bones (pa.) are much broader than long, 

 and form a very unsymmetrical pair, with an irregular median suture. They 

 are marked by a few coarse rugge, which tend towards a radiating arrangement. 

 The squamosals (sq.), which roof the usual posterior temporal fossa, extend 

 slightly further forwards than the parietals. The great smooth frontals (fr.), 

 which meet in a gently sinuous median suture in their hinder half, are remarkably 

 expanded in the interorbital region and suddenly taper in front to a very 

 slender rostrum, which terminates in a comparatively small mesethmoid (eth.). 

 The only traces of rugosity on these bones are on the longitudinal elevation 

 bounding the middle depression of the roof. There is a conspicuous, though 

 small, smooth postfrontal or sphenotic bone (fig. 2, ptf.) The parasphenoid bone 

 (as seen in a skull from Folkestone, in the Sedgwick Museum, Cambridge) is 

 toothless, and expanded into a thin flat lamina, which is widest just in front of a 

 sudden constriction where it passes into the floor of the suborbital canal. The 

 three postorbital cheek-plates (fig. 2, po.) are thin and nearly smooth, but bear a 

 few traces of shallow grooves radiating from the large slime-canal which traverses 

 their orbital border. The sclerotic is ossified. 



The mandibular suspensorium is inclined so far forwards that the gape must 

 have been relatively small, as shown by the position of the quadrate (qu.) in fig. 2. 

 The hyomandibular curves forwards and is very slender at its lower end, which 

 articulates with the rod-shaped symplectic. The latter element, of which the 

 lower end is seen in fig. 2, sym., penetrates a postero-superior cleft of the quadrate. 

 The jaws are unknown. The ceratohyal (fig. 2 a) is short and deep. 



The operculum and suboperculum (fig. 3) are nearly similar to those of the 

 type species, but somewhat more feebly ornamented. The preoperculum (fig. 2, 

 i»>j>.) is narrow, curves sharply forwards, and is marked on its smooth outer face 

 with the deep groove for the slime-canal. Five branchiostegal rays appear to have 

 been borne by the epihyal. The three upper branchiostegal rays borne by the cerato- 

 hyal are not much inferior to these in size. 



