ESPECIALLY MYCTOPHOIDS 105 
dorsally near to the uppermost region of the hyomandibular, and has a thickened 
anterior edge lying against the posterior edge of the hyomandibular crest. Ventrally 
the thickened edge of the preoperculum rests in a groove on the posterior thickened 
edge of the quadrate and is drawn out posteriorly into a prominent pointed spine. 
The preopercular sensory canal entered the bone through a dorsal pore and ran in a 
tube along the length of the bone, opening ventrally by two or three pores on or 
adjacent to the ventral spine. All of the visible openings are directed posteriorly, 
but the opening which transmitted the sensory canal to the mandible is usually 
hidden beneath the postero-dorsal upgrowth of the articular. The preoperculum is 
ornamented with the characteristic tubercles which are more prominent over the 
sensory canal. Posteriorly the preoperculum is thin and sparsely ornamented, 
although ventrally on the spine the tubercles are present on ridges of bone. 
The operculum has a slightly concave anterior edge which abuts against the 
posterior face of the hyomandibular. Dorsally the operculum is rounded but 
ventrally and postero-ventrally the edge is slightly concave. From the opercular 
facet on the anterior edge a horizontal strengthening ridge is produced which crosses 
the internal face of the bone to terminate on the lower posterior angle where it is 
extended as a short spine. The lateral face of the operculum is ornamented with 
bony tubercles which radiate out from the point of articulation with the hyo- 
mandibular. 
The suboperculum is large and dorsally lies internal to the ventral part of the 
operculum. Ventrally the suboperculum is more robust and bears tuberculated 
ridges, the dorsal region being more sparsely ornamented. 
Branchiostegal rays. There appear to be 14 or 15 branchiostegal rays, the first 8 
or g of which articulate with the ventro-lateral face of the ceratohyal, the tenth 
articulates with the region between the ceratohyal and epihyal, whilst the remaining 
4 or 5 articulate with the lateral face of the epihyal. The anteriormost rays, on the 
ceratohyal, are smaller and thinner than the subsequent ones, which are broader 
based, more widely separated, and taper more rapidly. The terminal branchiostegal 
ray is the broadest of the whole series and arises on a level with the ventral region of 
the preoperculum, curving postero-dorsally along the ventral margin of the sub- 
operculum. 
Pectoral girdle and fin. The pectoral girdle is shown in lateral view in Text-figure 
46. The post-temporal is horizontally arranged with an oval flattened upper limb 
articulating anteriorly with the epiotic. The dorsal surface of this upper limb is 
densely ornamented with raised bony tubercles. The ventral limb of the post- 
temporal is an elongated strut of bone, equal in length to the upper, which articu- 
lates antero-ventrally with the intercalar. The two limbs of the post-temporal join 
and the bone is produced posteriorly as a small vertical flange. A postero-medial 
facet is found on this flange and the facet contained the anterior region of the head 
of the supracleithrum. The lateral line canal passed within a tube through the bone. 
The anterior opening of the tube is clearly shown on the lateral face of the post- 
temporal. 
