WELLBURN : OS THE GENUS CCELACAXTHUS. 475 
roof is divided into a posterior or parieto-occipital (Pa.) and an anterior 
or frontal (Fr.) portion. These meet at an obtuse angle. The parieto- 
occipital moietie runs parallel to the base of the skull, whilst the 
frontal runs downwards to the snout, which is blunt and rounded, 
but none of the many specimens examined by the writer show any 
of the sutures by which this ethmoidal (E.) region was probably 
subdivided. 
The parieto-occipital region comprises a pair of large bones 
(Pa.), the parietals. These meet in the middle line, and are flanked 
postero-externally by a pair of triangular bones (Sq.), which appear 
to represent the squamosals fused with the post temporals. The 
frontal region comprises a pair of long narrow bones, which are 
divided down the middle line by a suture, and are flanked on each 
outer margin by a series of quadrate membrane bones — the para 
f rentals (Pa. Fr.) — whilst on each side, immediately posterior to the 
transverse suture which divides the bones of the cranial roof, are 
two small bones — the posterior frontals (P.F.). The orbit was 
large, prominent, and surrounded by a ring of delicate sclerotic 
plates, and was situated at a point about the junction of the anterior 
and middle thirds of the length of the cranial roof. Above are the 
para frontals ; in front there is a triangle-shaped bone which probably 
represents the fused anterior frontal and anterior orbital (A.O.) ; 
behind there is an irregularly shaped bone — the posterior orbital 
(P.O.). On the cheek, behind and below the latter bone, there are 
two triangular shaped elements, which appear to be the equivalent 
of the cheek plates of Megalichthys and Rhizodopsis. The upper- 
most of these two plates (X and XM is deeply triangular, and about 
twice the size of the lower one. From the anterior border of the 
larger cheek plate (X), commencing at a point a little above its an- 
terior inferior angle, a long narrow sub-orbital element (S.O.) runs 
forward below, then circling upwards in front of the orbit, joins 
the cranial roof bones above, whilst below this latter a long narrow 
bone, ornamented on its external surface, runs straight forward 
to the snout, from a point at the anterior inferior angle of the upper 
cheek plate. This latter bone (Mx.) is considered by Zittel and Reis to 
be the palatine, but, as pointed out by Huxley, " it has more the 
