90 UPPER CRETACEOUS TELEOSTS 
Opercular bones. The opercular apparatus is shown in lateral view in Text-figure 
39. The preoperculum is deep and narrow and curved somewhat forwards ventrally. 
It terminates dorsally below the head of the hyomandibular. The anterior edge of 
the preoperculum is thickened, this thickening is most pronounced in the ventral 
region, where the preoperculum abuts against the rear edge of the crest on the hyo- 
mandibular and the hind edge of the quadrate. The preoperculum widens ventrally 
and is produced into a short backwardly projecting spine. The preopercular 
sensory canal ran in a tube within the bone, opening dorsally by a single pore, and 
ventrally by three openings. Through the most anterior of these ventral openings 
the sensory canal passed into the mandible (B.M.N.H. number P.g250). The other 
ventral pores are directed more posteriorly. Laterally the preoperculum overlaps 
the anterior opercular region and bears an ornamentation of ridges and scattered 
tubercles, which are more pronounced on the ventral expanded area. 
The operculum is large and deeper than it is long. The facet for the opercular 
condyle of the hyomandibular is in the upper half of the bone. The dorsal and 
posterior margin of the operculum is smoothly convex. From the opercular facet 
on the anterior edge a horizontal strengthening ridge crosses the internal face of the 
operculum, terminating on the posterior edge. The lateral face of the bone is 
ornamented with radiating rows of tubercles. 
The suboperculum is large and deep, its dorsal part lying medial to the ventral 
part of the operculum. Antero-ventrally the bone is more robust and bears a 
10mm 
Fic. 40. Enchodus marchesettii (Kramberger). Pectoral girdle of the left side in 
lateral view. 
