OSTEOGLOSSID^. 
I i 
Head with opercular apparatus attaining a length of about 0*4. 
Length of head to preopercular border scarcely exceeding its 
maximum depth at the occiput; width of frontal region between 
the orbits equalling about half the total length of the cranium. 
External bones of cranial roof marlied with small pittings, the 
cheek-plates and opercular apparatus ornamented with radiating 
lines of very fine tubercles. Premaxilla extending to the anterior 
border of the orbit, at least two thirds as long as the more slender 
maxilla. Marginal teeth ovoid in transverse section, their longer 
diameter at right angles to the length of the jaw, and all the 
enamelled crowns smooth; teeth of premaxilla largest, teii in 
number; those of maxilla considerably smaller, between 20 and 
25 in number, decreasing in size backwards, where they become 
comparatively slender ; mandibular teeth about 20 in number, 
nearly as large as those of the premaxilla and scarcely decreasing 
in size behind. Operculum nearly twice as deep as broad. Anterior 
scales closely ornamented with very small tubercles often fused into 
short rugae. 
Form. Loc. Lower Eocene (London Clay): Sheppey, Kent. 
P. 3893. Imperfect head with opercular apparatus, to be regarded 
as the type specimen, partly shown of one third the 
natural size from the left side and from above in PI. I., 
figs. 1, la. The cranium is much fractured, the outer 
surface of the ethmoidal region, the greater part of the 
right frontal and of the parieto-occipital region being 
broken away. The frontals (/r.) are very wide between 
the orbits, narrowing behind, and they are much 
thickened, the outer surface preserved on the left side 
exhibiting numerous closely arranged pittings. The 
fossil has been broken across immediately behind the 
orbit, thus causing a gap in the left frontal; but its 
truncated posterior margin is conspicuous further back, 
well in advance of the occiput, and the corresponding 
suture on the right side is indicated by the direction of 
the growth-lines of the fractured bone. The anterior 
part of the left parietal (^a.) is shown to be superficially 
pitted in the same manner as the frontal; but the region 
beyond is obscure and more clearly observable in no, 
P. 157 (PI. 1. fig. 2). A very large and stout prefrontal 
is shown on the right side. The orbit (fig. 1, orh.) is 
indicated far forwards, and the great postorbital region 
is covered with two cheek-plates, which are very 
