externally and th e anterior end of the ectopterygoid internally; th e three bones being firmly bound
together. Posterior to the palatine, and in the same narrow space between the lachrymal and
ectopterygoid, a narrow rod of cartilage continues backward and soon expands .into a large flat piece
of cartilage which lies against th e inner surface of th a t p a rt of the ectopterygoid th a t bears the dermo-
ectopterygoid.
The second infraorbital bone is V-shaped, th e hollow of . th e V embracing the b luntly pointed
anterior end of the th ird bone of th e series. The hind end of th e dorsal limb of th e V is rounded, and
rests upon the external surface of the dermo-ectopterygoid. The hind end of th e ventral limb is
slightly grooved on-its -inner surface, a n d th is groove receives th e anterior end of a pointed anterior
process of th e quadrate, th e two bones being strongly bound together b u t a slight sliding movement
being permitted. The hind end of the second infraorbital, in some specimens, abuts against, while
in others it does n o t quite reach, th e anterior end of the ventral Hmb of th e preopercular. The main
infraorbital canal enters th e bone a t its anterior end, and leaves it a t the point of the angle between
its two limbs, one sense organ being found in th e section of canal so enclosed. On the outer surface
of the bone, near the middle of its length, there are two or three spines, these spines lying on the
horizontal ridge already described, and th a t ridge marking the course of th e latero-sensory canal
in th e bone.
The th ird infraorbital bone is large and somewhat parallelogrammic in shape. Its ventral
end is in contact with th e dorsal edge of th e v e n tra l limb of the second bone of the series, th e ventral
half of its anterior edge being in contact with th e postero-ventral edge of th e dorsal limb of th e same
bone. " The dorsal half of its anterior edge rests upon th e outer surface of th e dermo-ectopterygoid,
a small portion of th e la tte r bone coming to th e level of the outer surface of th e infraorbital bones,
being similarly marked with surface granulations, and appearing as a prolongation of th e dorsal
limb of the second infraorbital bone. The hind edge of the third infraorbital bone overlaps internally
and rests against th e anterior edge of the ventral half of th e preopercular. The anterior portion
of its dorsal edge is thickened, and bevelled on its inner surface, this bevelled surface having a sliding
articulation on th a t free ventral edge of the ectethmoid th a t lies posterior to th e posterior palatine
articular surface of th a t bone. The posterior portion of th e dorsal edge of th e infraorbital bone lies
internal to th e fourth infraorbital, the la tte r bone lying in a large depressed region on the external
surface of th e th ird bone. The bone is traversed by th e main infraorbital canal and lodges two sensory
organs of th e line.
The fourth infraorbital is a rhomboidal bone traversed b y the main infraorbital canal, and
lodging one organ of th a t line. I t forms almost the entire ventral margin of the orbit, overlaps
externally th e third infraorbital, and is bounded both anteriorly and ventrally by th a t bone. Posteriorly,
it overlaps externally and rests upon th e outer surface of a flange of th e hyomandibular, its
hind edge abutting against the anterior edge of the preopercular, and its dorso-posterior corner being
in contact with th e fifth bone of the infraorbital series. On its 'o u te r surface there is a low, sharp
and finely serrated longitudinal ridge, which lies superficial to, or slightly dorsal to the enclosed
section of th e latero-sensory canal.
The fifth infraorbital is a triangular bone th a t forms the hind margin of th e orbit and transmits
th e main infraorbital canal from th e fourth infraorbital to the postfrontal, lodging one organ of the
line. Its hind edge rests upon th e outer surface of the shank of the hyomandibular, and, in specimens
th a t have been preserved in alcohol, is so firmly attached to th a t bone th a t it appears in process
of ankylosis with it. Ventrally it is in contact with the fourth infraorbital. Posteriorly its ventral
half abuts against the dorsal portion of the anterior edge of the preopercular, its dorsal portion abutting
against th e anterior edge of the suprapreopercular bone. The dorsal end of the fifth infraorbital
does not quite reach th e lateral end of the postfrontal.
3. S U S P E N S O R I A L A P P A R A T U S A N D M A N D I B L E .
The PREOPERCULAR is a large, s tout and irregular bone. On its outer surface, slightly
below its middle point, there is a thin and relatively ta ll ridge, already referred to, which crosses
the bone horizontally, from one edge to the other, increasing gradually in height from in front backward;
and th a t p a rt of th e bone th a t lies ventral to th e ridge inclines ventro-mesially a t a marked
angle to th e p a rt th a t lies dorsal to it. The bone is traversed by the preopercular latero-sensory
canal, th a t canal presenting two straight limbs, a dorsal and a ventral one, which unite a t an
angle th a t lies beneath th e horizontal ridge on the outer surface of the bone. The canal lodges six
sense organs.
On th e inner surface of th e preopercular, following the angular course of the latero-sensory
canal, a flange arises from the bone, th e dorsal portion of this flange projecting antero-mesially and
th e ventral portion projecting dorsally or dorso-mesially, the two portions of the flange lying a t
th e same marked angle to each other th a t the two limbs of the latero-sensory canal do. In the angle
between the two portions of the flange there is a concave surface which lodges the cartilaginous inte rspace
between th e hyomandibular and symplectic. Dorsal to this concave surface, in the angular
space between th e dorsal limb of the flange and the internal surface of the anterior edge of the, bone,
this angle being presented anteriorly, the ventral three-fifths of the hyomandibular is lodged. Against
th e lateral, or dorso-lateral surface of th e anterior half of the ventral limb of the flange, the broad
fla t ventral surface of the posterior process of th e quadrate rests; both the quadrate and the hyomandibular
being firmly attached to the preopercular.
The HYOMANDIBULAR has, in alcoholic specimens, two dermal bones almost inseparably
fused with its outer surface. The lines of separation between these dermal bones and th e underlying
hyomandibular can be everywhere traced, b u t the two bones could n ot be removed, without breakage,
in any of th e specimens examined, all of which had been preserved in alcohol and then slightly boiled.
One of these two dermal bones is the fifth one of th e infraorbital series, and thè other the suprapreopercular.
As already stated, the hind edge of the fifth infraorbital bone rests upon th e lateral
surface of a flange on the anterior edge of the hyomandibular. This flange arises from a s tout longitudinal
ridge on the lateral surface of th e bone —'this ridge being th e homologue of the one already
described in the other fishes of the group — and between the flange and the anterior edge of the
body of the bone there is a V-shaped space, the hollow of th e V directed anteriorly and forming the
hind end of the flat space included, as in Trigla, betweén th e cheek-bones, externally, and the palatoquadrate
internally. In th e hollow of this V, near its ventral end, and hence anterior to th e longitudinal
ridge on th e lateral surface of the bone, th e canal for the hyoideo-mandibularis facialis opens,
having traversed th e bone from its internal surface. The longitudinal ridge on the lateral surface
of th e bone inclines backward, its summit fitting into th e V-shaped groove on the anterior edge of
th e dorsal limb of the preopercular. The fifth infraorbital was broken and picked off in the specimen
used for the figures.