moid, the recesses of opposite sides being separated by a thin wall of bone. The mesethmoid extends
entirely through the ântorbital cartilage, and presents, on the ventral surface of th a t cartilage, a median
circular surface which lies directly upon the parasphenoid; the vacuity found in this part of thè bone
of T. hirundo not here being present.
The parasphenoid has much the shape th a t it has, in T. hirundo, but the ascending processes
are well differentiated, and there is no median process in the interorbital region.
The basisphenoid has a sh o rt pedicle which descènds only about one half th e depth of the
myodome, and there terminates with a free end. This, free end gives a ttachment to th e middle point
of th e anterior edge of a s tout membrane which extends'backward and downward in th e middle line,
and laterally and slightly downward on either side, and has its insertion on th e floor and sides of the
myodome. This membrane separates th e myodome into two parts, a larger dorso-posterior portion
and a smaller antero-ventral one. The dorsal portion lodges th e rectus externus, th e ventral portion
lodging th e rectus internus. This membrane, judging from th e serial sections of th e several fishes
th a t I have examined, must be found in all teleosts, in a more or less developed condition. In Scomber
I have already described it (Allis, ’03, p. 92).
In other respects there are, in the cranium of T. lyra no important differences from th a t of
T. hirundo.
The hyomandibulo-palato-quadrate apparatus differs somewhat in shape from th a t ' of
T. hirundo, but in all important respects it closely resembles the apparatus of that fish. The lachrymal
is somewhat differently shaped, and its anterior edge is furnished with a number of stout sharp spines.
Two bones replace the large second infraorbital bone found in medium-sized specimens of T. hirundo,
thus making five bones, in all, in the series.
According to Günthër there are six bones in the series, but the specimens examined by him
must have been young fish, for in all of my specimens, which are large ones, there are but five bones..
The ridge th a t extends horizontally across the outer surface of the preopercular is much more pronounced
than in T. hirundo, and extends forward to th a t point of the third infraorbital boñe from
which the striae of the bone all radiate. The dorsal end of the preopercular is prolonged upward
and touches and is firmly bound to the outer surface of the hyomandibular, thus forming a closed
oval passage through which th a t part of the dilatator operculi th a t has its origin in the dilatator
fossa passes to reach its point of insertion on the opercular. The spine on the opercular, a t about
the middle of its hind edge, is much longer and stouter than in T. hirundo.
III. Peris tedion cataphractum.
1. S K U L L .
The orbital and postorbital portions, together, of the skull of Peristedion, occupy the posterior
half only of the total length of the skull, and the posterior third only of the total length of theskeletori
of the head. The anterior haljE of the skull is formed by the long, broad, flat and thin preorbital portion,
or snout of the fish, which is straight' and inclines slightly downward. The outer surfaces óf all thé
bones aïe finely granulated, the granulations being arranged, in certain places, but riot everywhere,
iri faintly indicated striae.
The flat anterior ends of the lachrymals form the so-called preorbital processes. These processes
are nearly as long as the snout of the fish, and their edges are finely serrated, each little tooth being
the end of a vein on the thin edge of the process, this vein appearing both on the dorsal and ventral
surfaces of the process as a slight and finely granulated ridge. At the base of the process two ridges
begin. The dorsal one is much the stronger and extends backward, across the cheek bones, as a longitudinal,
horizontally-projecting shelf, to the hind edge of the preopercular, where it terminates in
a tall, thin, obtuse and finely serrated hind end. The anterior half of the ridge bears two groups of
small point-like spines; a short anterior group, on the second bone of the infraorbital series, and a
long posterior one, on the third bone of the series. Dorsal to the ridge the outer surface of the cuirass
of the cheek inclines dorso-mesially, while, ventral to it, it inclines ventrally or ventro-mesially, the
ridge making a prominent angle on the outer surface of the cuirass. The ventral ridge is much less
important than the dorsal one, and lies near the ventral edge of the cheek bones. It, also, extends
to the hind edge of the preopercular, but it is always interrupted, as, or just before, it reaches the
anterior edge of th a t bone, and there usually breaks up into several slightly diverging ridges, all of
which are finely serrated their full length.
On the anterior quarter line, approximately, of the dorsal surface of the snout, at about the
middle of the length of the nasal bone, there is, on either side, either one stout vertical spine, or two
or more smaller spines lying one directly behind the other. On the posterior quarter line of the snout,
or even still nearer its base, there is, near the lateral edge of its dorsal surface, on the ectethmoid
bone, a group of from one to three similar but smaller spines. Postero-lateral to these latter spines,
there are, also on the ectethmoid, two or three short diverging lines of small tooth-like spines. The
dorso-mesial one of these lines is continuous with the dorsal edge of the orbit, th a t edge being
serrated. Slightly anterior to the transverse line of the ectethmoid spines, there is, on the dorsal
surface of the mesethmoid, a single large median spine.
Starting from the group of ectethmoid spines, on either side, a ridge runs backward to the
hind edge of the dorsal surface of the skull, traversing the ectethmoid, frontal and parieto-extra-
scapular bones. The ridges of opposite sides converge slightly, a t first, in a gentle curve, and then
run backward in slightly curved and slightly diverging lines to the hind end of the interorbital region,
when they again converge slightly to the hind edge of the skull. As they pass between the orbits
each ridge lies slightly mesial to the dorsal edge of the corresponding orbit. Each ridge bears a variable
number of spines, the spines that lie on the ectethmoid part of the ridge being small and sharply
pointed, while the others, on the frontal and parieto-extrascapular portions, are usually serratures
th a t increase gradually in size toward the hind end of the ridge. The large posterior serrature lies
on the parieto-extrascapular, extending the full length of th a t bone and ending almost directly
dorsal to the summit of the epiotic. The next anterior serrature is slightly smaller than the posterior
one, rises from the hind edge of the frontal, and extends across that part of the frontal th a t lies
posterior to the frontal commissure of the latero-sensory canals. The next anterior serrature is still
smaller, is sometimes double, and lies opposite and slightly posterior to the lateral end of the frontal
commissure. Beneath the base of this last serrature the sixth tube of the supraorbital canal passes,
on its way to join and anastomose with the main infraorbital canal at the edge of the frontal. The
fifth tube of the supraorbital canal has been suppressed, as in Scorpaena, the seventh or terminal
tube opening on the outer surface of the frontal slightly mesial to the point of this same serrature.
This third serrature from the hind end of the line thus has the position, relative to the supraorbital
Zoologica. Hoft 57. 18