NEORHOMBOLEPIS. 159 
constitute the middle part of the hinder border, which is straight and exhibits a 
wide, smooth surface of overlap for the supratemporals. The large frontal bones 
(fr.) ave very wide behind, and are an unsymmetrical pair. As shown in hinder 
view (fig. 1d), the occiput above the foramen magnum (/f.m.) 1s completely 
ossified, but its constitution is uncertain. The basioccipital (boc.) is largely 
excavated for penetration by the persistent notochord; and the basicranial axis, as 
far as the front of the orbit, is shown to have been parallel with the cramial roof. 
The cheek-plates are scarcely known, but they appear to have been more sparsely 
ornamented with tubercles of ganoine. One postorbital (fig. 1, po.) 1s deeper 
than broad. 
The mandibular suspensorium is vertical or slightly melined forwards. The 
inner face of the laminar pterygoid arch is covered with a cluster of small tuber- 
cular teeth, which pass at the lower border into very stout conical teeth nearly as 
large as those on the marginal bones of the jaws. The maxilla (fig. 1, ma.) is a 
long and narrow lamina, marked on the outer face with irregular longitudinal rugee, 
and sparsely ornamented with elongated tubercles of ganoine. — Its hinder half is 
excavated above to accommodate the long and narrow supramaxilla (sma.), which 
is similarly ornamented and is pointed at each end. The oral margin of the bone 
is nearly straight, and bears a regular close series of slender conical teeth, which 
are slightly curved inwards at the apex. The mandible (fig. 1, md.; fig. 1b) is 
slender, but elevated in the coronoid region, where a large surangular (saq.) 
articulates with the bifurcated end of the dentary 
. 
e 
Except near the oral border, 
the outer face of the dentary bone is more closely ornamented than that of the 
maxilla, and many of its tubercles are fused into longitudinal ridges. Its closely set 
teeth resemble those of the maxilla, but are perhaps stouter. The splemal bone 
is unknown. All the teeth are smooth, hollow cones, more or less tumid at the 
base, and usually capped with a small point of translucent enamel. ‘They are 
directly fused with the supporting bone, not in sockets. 
The opercular apparatus is only imperfectly known, but the operculum (op.) 
and suboperculum (sop.), with broad branchiostegal rays below, are seen in a 
fragmentary state on the right side of the fossil (fig.1). The operculum is deeper 
than broad, while the suboperculum is relatively large; and there are indications 
that the outer face of these bones was sparsely ornamented like the cheek-plates. 
Part of the large gular plate clearly shows such ornament. 
It is difficult to interpret the remains of the vertebral column, which are seen 
only in section; but the centra (fig. 1 ¢) appear to have been thin broad rings of 
loose and fibrous texture. 
The pectoral arch is not seen in the type specimen, but appended to it are 
post-clavicular plates (fig. 1, pel.). These are arranged as they usually appear in 
the Hugnathide, and the two lower plates exhibit a conspicuous ornament of 
tubercles and ridges directed antero-posteriorly. The surface of the two upper 
