. Bulletin of the British Museum (Natural History) Geology Supplement. go 1 ITER 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 produ
. Bulletin of the British Museum (Natural History) Geology Supplement. go 1 ITER 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 ( number ). 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 Fig. 40. Enchodus marchesettii (Kramberger). Pectoral girdle of the left side in lateral Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
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