34 
ACTINOPTEETGIl. 
Posterior suborbital plates radiately furrowed aud their extent 
exceeding one third the length of the skull; width of orbit much 
less than this measure ; teeth of premaxilla not larger than those 
of the maxilla, those of the mandible somewhat the largest. Width 
of opercular apparatus apparently not exceeding one third the 
length of the skull. 
Form. 4' Log. Turonian : S.E. England. 
37981. Type specimen, a vertically crushed imperfect head, shown 
of two-thirds the natural size in PI. Y. hg. 1 ; Lower 
Chalk, Hollingbourn, Kent. The cranial roof is well 
exposed but damaged by an oblique fracture. Its most 
characteristic feature is the median depression in the 
hinder frontal region, where the bone becomes com¬ 
paratively smooth. A trace of the small, finely-punctate 
supraoccipital (s.occ.) is observed at the hinder border of 
the depression, while quite posteriorly on the left side an 
otic bone (apparently epiotic, ejo.o.) is crushed outwards. 
The limits of the parietal {pa.)., squamosal {sp), and 
frontal {fr.) elements can also be distinguished; the last- 
named being relatively large bones, exhibiting a series 
of pits along either side of the depression where traversed 
by the slime-canal. The terminal ethmoid (etli.), finely 
punctate like the supraoccipital, is relatively small and 
pointed in front, without any expansion. The cheek- 
plates are best shown on the left side, where the posterior 
suborbitals ( 5 . 0 .) with their slightly radiating furrows are 
conspicuous. The sutures between these are not distinct, 
and it is not quite clear whether there is a border of cir- 
cumorbitals (c.o.) between them and the orbit. The anterior 
of the two circumorbitals above the orbit is relatively 
large and arched, curving downwards in front to meet the 
single long and narrow plate bordering the orbit beneath. 
There is also one small triangular antorbital plate {a.o.). 
The maxilla (m^.) is broken in front by a fracture and 
displacement which also crosses the mandible. It is over¬ 
lapped for about half its length by the supramaxilla 
(s.m.v.), which is a little expanded behind. The teeth 
in its anterior half are only about half as large as those 
in its posterior half. The premaxilla {pmoc.) is a thin 
triangular bone, sharply notched in its hinder border, 
and bearing a close series of teeth as small as those of the 
front part of the maxilla. The mandible is also delicate 
