canal, of the frontal spine of Scorpaena, b u t it does n o t lie a t th e hind end of the frontal, th a t
position being held by th e penultimate serrature of the - line. Whether this la tte r serrature
represents a p a rt of the frontal spine or not, I can n o t determine, b u t it apparently does. The
spine on the parieto-extrascapular must then be a parietal spine, and there is no nuchal spine.
Starting from or slightly postero-lateral to th e frontal spine, and running a t first postero-laterally,
and then posteriorly, near th e lateral edge of th e dorsal surface of th e skull, there is another
ridge, which corresponds in position to th e lateral row of spines of Scorpaena. This ridge has
a wavy or bluntly serrated edge and sometimes terminates, a t th e hind end of th e suprascapular,
in a small spine.
Emery (’85) has given a figure of the skull of the adult Peristedion in which th e spines th a t
I have ju s t described are roughly shown, with th e exception of the mesethmoid and ectethmoid spines,
which are neither shown in the figure nor mentioned in th e text. The spines are also shown b y the
same author in two figures of larvae of Peristedion of different ages, th e skull of the youngest larva
being said to so greatly resemble th e skull of th e ad u lt Scorpaena th a t Emery calls th a t larva the
scorpaenoid stage of th e fish. A t these two stages of Peristedion th e spines are all very large, and a
single spine on th e nasal, and a single large spine on th e frontal represent th e several spines on those
bones of the adult. A spine is also shown on the pterotic of th e youngest larva, this spine being wholly
wanting in the adult. Similarly, a spine is said by Emery to be found on th e nasal of the young of
Trigla hirundo, and to wholly disappear in th e adult.
The dorsal surface of the skull of Peristedion, between th e fronto-parietal serrated ridges,
and posterior to the frontal commissure, is perfectly flat, lies in a horizontal position, and corresponds
to the region of th e subquadrangular groove on th e vertex of Scorpaena. Lateral to th e ridge th a t
bounds this surface, on either side, the dorsal surface of th e skull is a flat surface th a t slopes rapidly
downward a t an angle of approximately 30° to the vertical plane. Between the orbits the dorsal
surface is concave. A low rounded ridge, on either side, here marks th e course of th e supraorbital
latero-sensory canal, the two ridges converging forward, in nearly straight lines, toward th e median
spine on th e mesethmoid. In th e preorbital region the lateral edge of th e dorsal surface of the skull
lies, as it does in Trigla, in the level of th e ventral surface of this p a rt of th e skull; and the line of
this edge, prolonged posteriorly, falls, in Peristedion, nearly into th e line of the lateral edge of the
postorbital p a rt of the dorsal surface of the skull.
The posterior surface of th e skull resembles th a t of Trigla b u t is steeper, and hence shorter
th a n it is in th a t fish. The hind edge of the secondary skull is sharp and finely serrated, and slightly
v entral to this edge, and parallel with it, there is a slight b u t sharp ridge which projects posteriorly
and forms a little shelf which gives support to the anterior edges of th e anterior row of the bony
plates of the body. The middle portion of th e shelf is formed by the supraoccipital, its lateral
portion, on either side, being formed by the parieto-extrascapular and suprascapular. Beneath the
ridge, or shelf, there is a slight median vertical ridge which represents th e spina occipitalis. This
little shelf in Peristedion is apparently simply th e ventral edge of the somewhat thickened hind end
of the secondary skull of the fish. Ventral to it there is a low and rounded transverse ridge which
represents what I have described in Scorpaena and Trigla as th e hind edge of the primary skull.
Between this ridge and the little shelf th a t represents the hind edge of the secondary skull, there is
a shallow groove which, although it here lies definitely on the hind surface of the skull, evidently
represents the supratemporal fossa.
The ventro-posterior limb of the supraoccipital extends ventrally almost to the dorsal margin
of the foramen magnum, being separated from th a t m argin by a median b it of cartilage. This exposed
b it of cartilage forms the hind end of a median band which separates the dorsal edges of the exocci-
pitals. The postero-lateral edge of th e skull, the edge th a t separates its posterior and lateral surfaces,
is thin, and projects ventro-laterally as a tall ridge. The ventral portion of this edge is formed by
the exoccipital and lies in a nearly horizontal position; its dorsal portion, formed by the posterior
process of the pterotic, lying in a nearly vertical position. Between these two portions there is a
large rounded corner formed by the opisthotic. This gives to the posterior surface of the skull a
flattened hexagonal appearance.
The temporal fossa is small and shallow, and on one side of one of the three specimens examined
was almost obliterated by the encroaching growth of th e bounding bones. The anterior portion of
th e fossa was especially affected by this contraction, b u t still remained as a small recess roofed by
th e small lateral extrascapular.
The dorsal surface of th e skull is formed, as in Trigla, by the nasals, mesethmoid, ectethmoids,
frontals, postfrontals, sphenotics, pterotics, parieto-extrascapulars, lateral extrascapulars and supra-
scapulars. All of these bones come to th e level of the outer surface of the skull, the exposed portions
of all of them being similarly marked by surface granulations. Slightly grooved lines mark most of
the ir contours. Anterior to th e nasals, and lying a t a b u t slightly lower level, there is a small rostral
depression. The floor of this depression is formed in p a rt by a narrow, thin and smooth projecting
plate of the deeper layers of either nasal, in p a rt by the ascending processes of the vomer, and in
p a rt by a small intervening portion of the cartilage of the rostrum. The mesethmoid is entirely
shut off, by th e nasals, from bounding relations to the depression.
The MESETHMOID has an exposed dorsal surface th a t is usually somewhat lenticular in
shape, and th e stout, median, mesethmoid spine rises from it, slightly anterior to its middle point.
Beneath the superficial, dermo-perichondrial portion of th e bone there is a primary portion, of less
extensive surface, which extends completely through the cartilage of th e snout. In its deeper portion
this primary component expands, and becomes a circular p late formed around a p oint th a t lies directly
beneath th e median mesethmoid spine. Between this circular basal plate of th e bone and the dorsal
dermo-perichondrial plate, there is, on th e lateral and posterior edges of th e bone, a deep groove;
the grooves on the lateral surfaces of th e bone being exposed laterally, b u t the one on the posterior
surface lying within the cartilage of the skull.. The lateral edge of the dermo-perichondrial component
of th e bone suturates with the mesial edge of the corresponding component of the ectethmoid, a canal,
large anteriorly b u t small posteriorly, being left between the two bones; the canal lying pa rtly between
the primary components and p a rtly between the deeper layers of th e dermo-perichondrial
components of th e bones. The smaller, posterior portion of this canal transmits the supraorbital
latero-sensory canal and the ramus ophthalmicus superficialis; the larger anterior portion tran s mitting
th a t same canal and nerve, and also th e nervus olfactorius. A varying number of openings,
between the ethmoid bones, lead from the canal to the outer surface of the skull, b u t they are all
closed externally by membrane. Anteriorly the mesethmoid suturates with the nasal bones, and
posteriorly with th e frontals. Ventrally, its primary portion lies directly upon the dorsal surface
of th e parasphenoid, the two bones being so firmly attached to each other th a t they would seem
to be in process of ankylosis.