464 GLYPTOLEMUS KINNAIRDI 
[Plate 33] though the lines of demarcation between its constituents are 
not visible. Posteriorly, it is broad and expanded, furnishing the con- 
dyle to the mandibles by its outer and lower margin, while its upper 
and inner part probably abutted against the sphenoid. Anteriorly, 
it rapidly narrows, and is continued forwards as a strong bony bar. 
Running parallel with and outside this, is a second elongated bony 
ridge, which may be distinct from the foregoing, or may be only the 
outer part of it. At any rate, the two seem to become one in front, 
Here they support a very strong tooth, and there is a second large 
tooth situated far back upon the outer bone. 
This palato-quadrate apparatus, taken altogether, very much re- 
sembles that of Lefzdosteus in form, and in the large teeth which it bears. 
The contour of the stout mandible follows that of the head, the 
gape extending as far back as the level of the posterior edges of the 
parietal bones. The rami are very stout, but appear to have consisted 
of only a thin osseous shell, sculptured externally in the same way as 
the cranial bones. The constituent elements of the mandible are not 
distinctly separated from one another in any specimen. 
The jugular plates consist of two principal and a number of lateral 
scale-like bones. The former are elongated, nearly right-angled, tri- 
angles, with their perpendiculars turned towards one another, and their 
apices engaged in the re-entering angle of the rami, while their bases 
are situated midway between the articular ends of the rami and the 
posterior margins of the opercular apparatus. The peculiar sculpturing 
of these plates gave rise to the name of the genus, and is well shown 
in fig. lv, Plate II. [Plate 34]. The outer edges of the principal jugular 
bones lie close to the inner edges of the rami of the mandible anteriorly, 
but posteriorly a space is left between them, which gradually widens 
posteriorly, and is so continued between the suboperculum and the 
posterior part of the principal jugular plate. This interval is filled up 
by the secondary jugular plates, of which, in one specimen, I count 
five, gradually increasing in size from before backwards. All these 
plates exhibit the characteristic surface ornamentation, and the last, 
much larger than any of the others, extends beyond the level of the 
posterior margin of the principal jugular plate, its curved free margin 
sweeping backwards and outwards, and lying between the sub- 
operculum and the pectoral arch, while a considerable portion of the 
bone seems to pass under and be overlapped by the suboperculum. 
There is no median rhomboidal intercalary bone between the anterior 
and inner edges of the principal jugular bones. 
The ventral part of the pectoral arch is represented, on each side, 
by two broad, triangular, somewhat curved, bones. The anterior one 
