184 UPPER CRETACEOUS TELEOSTS 
The articular forms the posterior region of the mandible, extending anteriorly to 
insert on the medial face of the dentary. Below the shallow articular facet there is a 
small posteriorly directed foramen which transmitted the mandibular sensory canal. 
This sensory canal passed within a tube of bone on the ventro-lateral edges of both 
the articular and dentary, and a small oval pore close to the symphysis indicates its 
anterior extent. The lateral face of both dentary and articular is unornamented, 
but the articular has a pronounced lateral flange passing forwards from in front of 
the articular facet. This flange decreases in size and ends near to the level of the 
posterior end of the premaxilla. The maxilla rests against the dorsal surface of this 
flange when the jaws are shut. 
The angular is a small knob of bone forming the postero-ventral angle of the 
mandible, with its posterior face fitting against the ventral region of the pre- 
operculum, 
Opercular bones. The opercular bones are shown in lateral view in Text-figure 84. 
The preoperculum is deep, and narrow. Dorsally it ends posterior to the head of the 
hyomandibular and anteriorly lies against the posterior face of the crest on the hind 
edge of the hyomandibular. Ventrally the preoperculum rests in a groove on the 
posterior edge of the quadrate, where it is slightly expanded and bears several promi- 
nent ridges. The preopercular sensory canal ran within a tube along the length of 
the bone opening ventrally through three or four pores. The most prominent pore 
faces antero-ventrally and transmitted the main canal to the mandible. The 
posterior edge of the preoperculum is thin and overlaps the anterior edge of the 
operculum. 
The operculum is large and the opercular facet occurs just within the upper half of 
the anterior edge. The posterior edge of the operculum is rounded dorsally, but 
ventrally the edge is irregularly excavated. A horizontal strengthening ridge passes 
across the internal face of the operculum. 
The suboperculum lies ventral to the operculum and is overlain by the latter to a 
marked extent. The supoberculum has a smooth outline, unlike the operculum, 
and its lateral face is unornamented. No trace of an interoperculum was found in 
any of the specimens examined. 
Hyoid arch. Both the ceratohyal and the epihyal are elongate, roughly rectangular 
ossifications, joined in life by cartilage. A prominent groove runs along the length 
of the lateral face of both bones and marks the course of the hyoidean artery. The 
hypohyals are prominent and attached to each other in the mid-ventral line. The 
ceratohyal is firmly attached to the posterior end of the hypohyal, and traces of a 
median urohyal are seen where it contacted the hypohyals. The urohyal is elongate 
with a shallow dorsal longitudinal crest. 
Fourteen branchiostegal rays are present, the first 8 attached to the ventral region 
of the lateral face of the ceratohyal. These 8 rays are uniform in size and shape. 
The more posterior 6 branchiostegal rays articulate with the epihyal and are stouter, 
slightly flattened and more sharply inclined posteriorly. 
