112 UPPER VCRELAGE OUS LE LEOSRS 
cranium of Enchodus lewesiensis. Apart from the size difference the cranial roof is 
practically identical to that of Eurypholis boissieri. In order to elucidate these 
points a second specimen was prepared in acid, P.10984, from the Holaster sub- 
globosus zone of Hitchin, Hertfordshire. This, like the holotype, was exposed from 
the right side. The neurocranium which was recovered after acid treatment was 
incomplete only in respect of the roof region. Thus using the two specimens P.1703 
and P.10984 a complete description of the neurocranium and jaws was obtained. 
Although the body is missing from both specimens, the head supplies ample justifica- 
tion for transferring the species to the genus Ewrypholis. 
DESCRIPTION. Neurocranium. The neurocranium is shown in dorsal, ventral, 
lateral and posterior views in Text-figures 49-52. The cranial roof is flattened and 
attains its widest point behind the orbits in the sphenotic region. The frontals cover 
practically the whole of the skull-roof and meet in the mid-dorsal line in a straight 
suture. The interorbital region of the skull-roof is slightly depressed and more 
sparsely ornamented. The frontal contacts the dorsal surface of the sphenotic and 
spreads partially above it. The entire roof is covered by an ornamentation of raised 
tubercles, and where the sensory canals passed within the bone the ornamentation is 
accentuated, the tubercles being raised on bony ridges. The ornamentation 
radiates outwards from the centre of ossification. Anteriorly the frontals taper from 
in front of the orbits and are inserted into the rear edge of the mesethmoid. Postero- 
laterally the frontal contacts the pterotic, and posteriorly the parietal and the 
supraoccipital. 
The supraoccipital is a small median bone contacting the frontals anteriorly and 
separating the parietals. In the mid-line of the posterior face of the supraoccipital 
is a small backwardly directed crest. 
The parietals are narrow, transversely elongated strips of bone. Anteriorly the 
parietals are bordered by the frontals and posteriorly by the epiotics. The tuber- 
cular ornamentation of the frontal bone is continued on to the parietal and the 
supraoccipital. A shallow groove present on each parietal bone is continuous 
with a shallow transverse groove on the supraoccipital. Behind the transverse 
groove on the parietal the hind border of the skull-roof is composed of a further strip 
of the parietal bounded posteriorly by the epiotic. This posterior part of the 
parietal is unornamented, probably indicating that the epaxial musculature en- 
croached on to the postero-dorsal surface of the skull-roof. 
The pterotic forms the postero-lateral border of the skull-roof, joining the sphenotic 
anteriorly, the frontal and parietal medially, and the epiotic posteriorly. The dorsal 
surface of the pterotic is heavily ornamented, the tubercles being joined by inter- 
vening ridges of bone to give an irregular latticed appearance. 
The sphenotic forms the postero-dorsal region of the orbit and contacts both the 
frontal and the pterotic. The dorso-medial region of the bone is ornamented 
similarly to the pterotic, but more laterally the surface becomes smoother. 
The course of the sensory canals on the skull-roof is indicated by tubes within the 
bone and open grooves on the surface. The supraorbital sensory canal passed for- 
wards within the frontal and emerged anteriorly on the lateral edge of the frontal. 
