ESPECIALLY MYCTOPHOIDS 143 
Mandible. The dentary forms the major part of the mandible and has a V- 
shaped posterior indentation. The symphysial region is considerably constricted 
but posteriorly the dentary is deep. The oral border supports a dense cluster of 
small acutely pointed teeth. Whether these teeth were arranged in definite rows 
could not be ascertained, although there is a distinct row of minute conical teeth 
on the extreme oral edge. This marginal row of teeth resembles that on the 
dermal upper jaw, whereas the more internal teeth are similar to those on the palato- 
pterygoid. 
The articular forms the posterior part of the mandible and has a shallow, trans- 
versely orientated facet. On the postero-lateral surface a small pore, just below 
and behind the articular facet, transmitted the mandibular sensory canal. The 
sensory canal ran within the articular and opened into a deep groove anteriorly. 
This groove is continued on the ventro-lateral part of the dentary. Along much of 
its length on the dentary the groove is covered by a dorsal flange of bone. 
The lateral surface of the mandible is ornamented with minute tubercles. Above 
the sensory canal groove the tubercles radiate backwards from the symphysis, but 
below the groove the tubercles are much less prominent and regular. The articular 
ornamentation is confined to the region below the articular facet. 
The angular is a small knob of bone attached to the postero-ventral region of the 
articular and is strongly ornamented with bony tubercles. 
Opercular bones. The preoperculum is deep and narrow and vertical in position. 
Dorsally the preoperculum ends below the upper limit of the hyomandibular. The 
anterior edge of the preoperculum lies against the posterior face of the crest on the 
hyomandibular and ventrally abuts against the posterior edge of the quadrate. 
The ventral extremity of the preoperculum is slightly broadened. The preopercular 
sensory canal ran within a groove in the upper half of the bone, but in a definite tube 
more ventrally. This tube opens anteriorly at the lowermost extremity of the 
preoperculum beneath the quadrate condyle. The lateral face of the preoperculum 
is liberally ornamented with minute tubercles. 
The operculum has a straight, vertical anterior edge and the opercular facet 
occurs approximately one-third of the way down. Dorsally and posteriorly the 
operculum is rounded, but ventrally the edge is obliquely inclined. From the 
articulatory facet a horizontal strengthening ridge extends back across the inner face 
of the operculum. The operculum is ornamented with bony tubercles which 
radiate from the region of the opercular facet. The tubercles are absent from a 
narrow region anteriorly and antero-dorsally. 
The suboperculum is large and deep with its dorsal edge lying medial to the 
operculum. From the antero-dorsal region of the suboperculum a small projection 
extends dorsally. The whole anterior edge of the suboperculum is thickened but 
the remainder, like the operculum, is thin. Externally the characteristic tubercles 
are arranged randomly. 
A small, ornamented interoperculum is present beneath the ventral extremity of 
the preoperculum and suboperculum. 
