214 UPPER CRETACEOUS TELEOSTS 
meets the articular in a straight suture. The upper limb of the dentary forms the 
tooth bearing margin of the jaw, the teeth being borne on a stout medially directed 
flange. The teeth are present in three major rows and are similar to those on the 
upper jaw. 
The articular forms the posterior jaw region and has a shallow, concave, trans- 
versely arranged facet. The articular is produced behind the facet into a small 
retroarticular process. The mandibular sensory canal runs within the articular and 
opens on to the surface through several pores. The dorsal part of the articular is thin 
although the posterior edge is thickened. 
The angular is a small knob of bone applied to the extreme postero-ventral surface 
of the articular. 
Operculay bones. The opercular bones are shown in medial and lateral view in 
Text-figures 89 and go. The operculum is reduced in extent whereas the sub- 
operculum is greatly expanded. The operculum has straight anterior and dorsal 
edges, but is rounded posteriorly. The lateral face of the bone is completely smooth. 
The opercular facet is prominent, and near to the dorsal end of the anterior edge of 
the operculum. The facet is supported by an oblique flange crossing the internal 
face of the operculum. 
The suboperculum is greatly expanded forming the entire posterior edge of the 
opercular cover. Its dorsal border lies medial to the ventral and posterior edges of 
the operculum, and a large pointed process from the antero-dorsal corner extends 
upwards medial to the operculum. The anterior edge of the suboperculum is 
thickened and overlaps the posterior edge of the interoperculum medially. 
The interoperculum is roughly triangular with a vertical posterior edge. It 
ends anteriorly just behind the angular region of the mandible. 
The preoperculum is large and curved forwards ventrally. The dorsal termination 
of the preoperculum lies immediately above the opercular process. Dorsally the 
leading edge rests against the hyomandibular crest, but below the crest the edge of 
the preoperculum expands anteriorly to overlap the lateral face of the ventral end 
of the hyomandibular. Ventrally the preoperculum lies against the posterior edge 
of the quadrate. The preopercular sensory canal runs within a tube in the centre 
of the lateral face of the preoperculum, and gives off large posteriorly directed pores 
for subsidiary branches of the canal. The extreme posterior edge of the preoper- 
culum lies over the anterior edges of both the operculum and suboperculum, and 
covers much of the interoperculum. On the ventral part of the preoperculum the 
sensory canal tube opens by three large pores. The anteriormost opening is directly 
behind the retroarticular process of the mandible. 
Hyoid arch and branchiostegal rays. The hyoid arch consists anteriorly of a large 
ventral hypohyal and a smaller dorsal hypohyal connected to it by cartilage. The 
ceratohyal is long and shallow, whereas the epihyal is shorter and triangular. A 
small mesially constricted interhyal connects the epihyal to the interspace of cartilage 
at the base of the hyomandibular. Both the ceratohyal and the epihyal have a 
continuous groove on their lateral faces for the hyoidean artery. A median, 
vertically arranged urohyal extends posteriorly from its connection with the ventral 
