PACHYCORMIDZE. 
381 
insignificant. Pin-fulcra minute or absent. Pectoral fins large and 
sickle-shaped, the rays only branching and articulated at the 
extreme end; pelvic fins absent; dorsal in advance of the anal fin, 
which is not much extended ; caudal fin very deeply forked. Scales 
small and very deeply imbricating, those of the ventral aspect 
scarcely broader than deep ; lateral line conspicuous. 
The most characteristic feature in the skull of this genus is the 
median elevation of the parieto-occipital region, which affects a 
sharply-defined triangular area at the hinder end of the cranial 
roof. The roof-bones themselves appear to be all fused together 
into a continuous shield, and the surface is completely covered with 
a very fine granular ornament. Traces of the sutures between the 
frontals, squamosals, and parietals are, however, sometimes seen ; 
and the frontals are thus shown to form the greater part of the 
hinder elevation. The elements in the otic region are well ossified, 
though not hitherto precisely determined; but there appears 
to be no ossified interorbital septum. The parasphenoid, when 
viewed from the side, is observed to be gently arched, bulging 
slightly downwards; while the vomers seem to be completely 
fused with the mesethmoid. Of the facial bones, by far the largest 
and most conspicuous are two suborbitals (postorbitals), which 
occupy nearly the whole of the cheek between the preoperculum 
and the orbit. The circumorbitals are comparatively small, and 
have only been satisfactorily observed as a series of little plates, 
all broader than deep, on the anterior border of the suborbitals. 
The sclerotic capsule is ossified. The maxilla is long and slender, 
tapering in front, deepest behind ; and its hinder margin is exca¬ 
vated to receive a large, short, and deep supramaxilla, which does 
not extend upwards on the cheek higher than the maxilla itself. 
The premaxilla has not been observed, and may perhaps be fused 
with the rostrum. The structure of the mandible is not vet satis- 
factorilv known; but the splenial is evidently a delicate plate with 
comparatively minute teeth, while the angular bone occupies only a 
short extent of the outer face of the ramus. 
There is a large gular plate completely covering the anterior 
portion of the space between the mandibular rami, while the 
branchiostegal rays are short and numerous, often as many as 50. 
Of the opercular apparatus the most characteristic feature is the 
very large size of the suboperculum, which is trapezoidal in form and 
throws sharply forwards the apex of the triangular operculum. 
The preoperculum and interoperculum are narrow and comparatively 
small. The supratemporal plates resemble those of Amici. 
The notochord must have been always persistent, though there 
