II. Sebastes dacty 1 opterus.
The skull of Sebastes dactylopterus is relatively taller and shorter than th a t of Scorpaena
scrofa; the orbits being relatively larger, the interorbital region narrower, the antorbital region shorter,
and the mid-dorsal line considerably more convex than in the latter fish. The space between the eyes
is concave.
The ventral surface of the skull, starting immediately posterior to the dentigerous ridge on the
ventral surface of the anterior end of the vomer, is slightly convex, the summit of the convexity
lying beneath the foot of the basisphenoid.
The internasal ridge is similar to that in Scorpaena, but the mesethmoid processes are smaller
and project almost directly forward instead of forward and upward. The bases of these processes
are connected by a curved transverse ridge, concave anteriorly, against the anterior surface of which
the hind end of the internasal ridge abuts and ends. Against the wide and slightly concave lateral
surface of each process the corresponding nasal rests, th a t bone being firmly bound to the process and
bearing, on the dorsal surface of its hind end, the nasal spine.
Immediately lateral to the base of the mesethmoid process, there is a large aperture which
lies between the ectethmoid below and the anterior end of the frontal above. This aperture is the
anterior opening of th a t section of the supraorbital latero-sensory canal th a t lies in the frontal, combined
with the anterior opening of a small canal, between the ectethmoid and the. frontal, th a t
transmits the rami ophthalmicus lateralis and ophthalmicus trigemini. Starting from this aperture,
a large rounded ridge runs backward between the orbits, curving a t first slightly toward the middle
line and then diverging slightly from it, and marking the course of the supraorbital latero-sensory
canal. Beginning slightly posterior to its anterior end, the ridge bears on its dorsal surface a narrow
ridge th a t runs posteriorly, concentric with the dorsal edge of the orbit, and, gradually increasing in
height, terminates in a spine. This spine lies posterior to the transverse commissure formed by the
fusion, in the middle line, of the fourth primary tubes of the supraorbital canals of opposite sides,
and overhangs the seventh or terminal tube of the supraorbital canal. I t is accordingly the frontal
spine of the fish, and the narrow ridge th a t terminates in it is the frontal spinous ridge. The third
primary tube of the supraorbital canal opens on the dorsal surface of the frontal, lateral to this frontal
ridge, a t about the middle point of the orbit.
The hind border of the supraorbital commissure is marked by a slight ledge, th a t part of the
dorsal surface of the skull th a t lies posterior to the ledge lying a t a slightly deeper level than the
part th a t lies anterior to it. The frontal spinous ridge, curving postero-laterally, crosses the lateral
end of the transverse ledge, and a t this point, or from the mesial surface of the frontal ridge slightly
posterior to it, the parietal spinous ridge begins. Running backward and slightly laterally from there,
the parietal ridge terminates in the parietal spine, th a t spine lying directly above the supratemporal
cross-commissural canal. The anterior end of the parietal ridge lies on the hind edge of the frontal,
the remaining and larger part of it lying on the parieto-extrascapular. Immediately posterior to the
parietal spine, a short ridge begins on the dorsal surface of the extrascapular part of the parieto-extrascapular,
and, continuing the line of the parietal ridge, terminates, a t the hind end of the skull, in the
nuchal spine.
The nasal, frontal, parietal and nuchal spines of Sebastes thus form a row of spines on the dorsal
surface of the skull that is strictly comparable to the middle row of spines in Scorpaena, but, as will
be explained .below, the frontal spine has been displaced laterally to such an extent th a t it might
be mistaken for one of th e lateral row of spines.
The p arietal spinous ridge and th e transverse commissural ledge boiind laterally and anteriorly
a flat smooth median portion of th e dorsal surface of the brain case, this surface lying a t a slightly
lower level th a n the anterior p a rt of th e dorsal surface of the skull. This flat and slightly depressed
surface thus certainly represents a slightly developed subquadrangular groove on the vertex of the
skull of th e fish, notwithstanding th a t Günther (’60, vol. 2, p. 95) says th a t all members of this family
are without th a t groove. Posteriorly, this slightly developed groove is bounded by a slight transverse
ridge which lies on the dorsal surface of the parieto-extrascapular of either side, near its hind edge.
This ridge extends to the mesial edge of either parieto-extrascapular, b u t as these bones do not meet
in th e middle line, the ridge does n o t extend entirely across the hind edge of the sk u llK Th e ridge
marks the course of a portion of th e supratemporal commissure, the m edian portion of th a t commissure
lying in th e dermal tissues, between the ridges of opposite sides, in a slight groove on the flat dorsal
surface of th e supraoccipital. The slightly depressed surface th a t represents the subquadrangular
groove is thus not bounded posteriorly by à complete ridge, as in Scorpaena, simply because the
median portion of th e supratemporal commissure is not here enclosed in bone.
The lateral row of spines is represented by five spines. The anterior spine of the row is the
preocular spine, lying on that edge of the ectethmoid th a t forms the anterior portion of the roof of
the orbit. The next two spines of the row are the supraocular and postocular ones, both of which lie
close together, one directly behind the other, on the dorsal surface of the roof 'of the orbit, near its
latéral edge, and immediately anterior to the frontal spine. In the specimen used for illustration the
postocular spine is bifid on one side of the head, and, anterior to the supraocular spine, there is a small
additional spine. The supraocular and postocular spines, as normally found, together with the frontal
spine form a short line of three spines lying close together and equidistant one from the other, and
they correspond in position to the supraocular, postocular and tympanic spines of Jordan & Gilbert’s
diagram of the spines in Sebastodes. The frontal spine however belongs, as just above described,
to the middle row of spines and not to the lateral one. The remaining two spines of the lateral row
are small ones th a t hardly rise above the outer surface of the bodyj one of them lying on the hind
edge of the suprascapular and the other on the hind edge of the supraclavicular. On the pterotic
there is a ridge, but it does not end in a spine.
The intermediate row of spines is represented by a small spine on the hind eige of the epiotic
process of the suprascapular, this spine lying slightly mesial to the suprascapular spine of the lateral row.
The bones of the snout of Sebastes differ in no important respect from those of Scorpaena
scrofa. The mesethmoid processes, as already stated, are shorter than in Scorpaena, and are directed
forward instead of upward and forward. The nasals are traversed by the supraorbital latero-sensory
canal, and are relatively larger than in Scorpaena. The lateral arm of the ectethmoid is not differentiated
from the wing of the bone, as it is in Scorpaena, the ventral edge of the wing being simply
thickened and giving articulation, by two articular surfaces, to the lachrymal and palatine. The
vomer has, on either side, an ascending-process,-which gives articulation, as in Scorpaena, by the
intermediation of a disk of semi-cartilaginous tissue, to the ascending process of the maxillary. The
maxillary has a right-angled ascending process and a ligamentary process, the former articulating
both with the premaxillary and the vomer, and the latter giving support to the lachrymal and palatine,
as in Scorpaena. The rostral is more deeply grooved on its ventral surface than in Scorpaena.