156 FOSSIL FISHES OF THE ENGLISH CHALK. 
for sutural union with the nasal bones (ia.). In the fossil these elements are 
slightly displaced, but they are shown to be longer than broad, and they must 
have met originally in the middle line. Hach nasal bears a small rounded boss of 
enamel near its antero-external angle. The skull is completed in front by a short, 
broad and rounded bone, in which the two premaxille are fused probably with 
a small mesethmoid (fig. 4, pme.; fig. 4c). The cheek-plates are scarcely known, 
but among displaced fragments there seems to be an antorbital (fig. 4, ao.), which 
bears a rounded boss of enamel near its antero-inferior angle. 
The mandibular suspensorium must have been nearly vertical, and the gape 
of the mouth is as wide as in Amia. The imner bones are unknown; but one 
regular series of small conical teeth within the maxilla was probably borne by the 
ectopterygoid, while similar teeth in front belong either to the palatine or vomer. 
The fused premaxille (figs. 4, 4a, pmw.; fig. 4c), which are very coarsely 
ornamented, form a broad and bluntly rounded snout, with a single regular series 
of about twelve stout, conical teeth. The maxilla (figs. 4, 4, mv.) is stoutest and 
most coarsely ornamented in front, becoming a wide tuberculated lamina behind. 
The oral margin is nearly straight, very shehtly wavy in the middle (broken on 
the right side of the fossil, fig. 4), and bears a single series of conical teeth, 
which are smaller than those of the premaxilla and become minute behind. The 
mandibular rami are especially stout, and the peculiar shape of the ramus of the 
left side is shown from below and in outer view in fig. 44. The dentary bone (d.) 
forms nearly the whole of its outer face, on which the tubercular ornament is 
in many parts fused into vermiculating ridges. It bears a single regular series 
of conical teeth, which are much larger than those of the upper jaw and do not 
diminish in size backwards. Within the entire length of the dentary there is a 
single series of minute conical teeth (perhaps the front series of a cluster), which 
doubtless belong to a splenial element and extend behind up the slight coronoid 
elevation. All the teeth are hollow cones capped with a point of translucent 
enamel; and the large mandibular teeth exhibit a feeble vertical fluting in the 
apical half. They are directly fused with the supporting bone, not in sockets. 
The preoperculum (fig. 4, pop.), is narrow and gently arched, with the large 
lower limb blunter than the upper limb, and the angle marked only by a broad 
horizontal ridge. ‘The tubercles of its ornament are antero-posteriorly elongated 
(fig. 4d). The operculum (fig. 4, op.) must have been about as broad as deep, with 
its lower border straight and nearly horizontal, and its upper portion rapidly 
tapering by the truncation of its postero-superior angle. The ornament of its 
outer face is for the most part fused into a coarse reticulation. The sub- 
operculum (fig. 4, sop.) 1s very broad and not deep; the elongated tubercles of its 
ornament incline downwards and backwards, and cause its border to be pectinated. 
A fragment of the interoperculum shows that this element was also highly 
ornamented. There are remains of thirteen branchiostegal rays (fig. 4, br.), of 
