GLYPTOL.EMUS KINNAIRDI 463 
maxilla, the nasals and the frontals below, in front and above, and 
apparently, with the post-frontal behind. Their posterior excavated 
margins form the anterior boundary of the orbit. 
The post-frontals, better defined posteriorly than anteriorly, appear 
to join the prefrontals, and then, extending backwards beyond the 
posterior margins of the frontals, they unite with the anterior moiety 
of the parietals, filling up all that notch in the outer border of these 
bones, which has been described. Their posterior edges are con- 
nected, internally, with the anterior margins of the projecting part of 
the parietal, externally with the same margins of the small quadri- 
lateral squamosal bones. 
The posterior part of the supero-lateral region is completed by two 
squamiform bones, which take the place of the external occipital, or 
epiotic, bones of other fishes, filling the interspaces left between the 
supraoccipital and the opercular apparatus. The inner surface of this 
bone, on the left side, presents a very well marked triradiate impression, 
one crus of which is directed transversely inwards, while the others are 
respectively directed forwards and backwards. A shallow groove upon 
the surface of the supraoccipital, which has a slight concavity forwards, 
connects the transverse crus of the impression on one of these bones 
with that on the other. 
The triradiate marks are much more distinct upon the inner surface 
of these bones, where they form distinct ridges, than upon the outer 
surfaces, where they appear only as very shallow and indistinct grooves ; 
and, except for the continuation of each transverse crus into its fellow 
across the supraoccipital, I should have been disposed to connect them 
rather with the semicircular canals of the auditory organ than with the 
so-called mucous grooves. 
The lateral regions of the skull behind the premaxillaries are 
formed, in front of the orbit, by the prefrontal and maxillary, and 
behind the orbit, first, by the maxilla and a large postorbital bone, then 
by the maxilla, by the bone marked P. O., which may very likely not 
be a true preoperculum, and a large supratemporal bone. The latter 
articulates above with the postfrontal and squamosal, and fits posteriorly 
into the notch formed by the vertical and horizontal portions of the 
bone P. O. 
The operculum, a large four-sided bony plate, is connected with 
the outer edge of the epiotic above and with the posterior edge of the 
ascending ramus of the bone P. O. in front. Its lower edge articulates 
with the upper margin of the suboperculum, which is about half as 
large as the operculum, and has a much more rounded posterior edge, 
The palato-quadrate arcade is best exhibited in fig. 1a, Plate I. 
