TRIASSIC FISHES FROM SPITZBERGEN 
67 
In W. sinuosa the postorbital ( Po , text fig. 25; PI. 5, figs. 2, 4; PI. 6, figs. 1, 2) has 
a somewhat rounded quadrangular shape and is a little broader than it is high. Its 
posterior margin is convex, its anterior margin is concave; its lower margin is straight 
or very slightly convex and so is also its dorsal one with the exception of the part 
farthest forward, where there is a well marked sinus. The antero-dorsal corner is extended 
to a broad, obtuse process. The antero-ventral corner forms a pronounced angle while 
the postero-dorsal as well as the postero-ventral ones are well rounded off. Near the 
antero-ventral corner the anterior margin has a blunt little process and one or a pair of 
lines and shading. From P. s5 7. 3 l t . 
Co, coronoid; De, dental; Fr. dsph, fronto-dermosphenotic; G, jugular plate; La. ju, lacrvmo-jugal; Mx, maxillary; Na. ant, nasalo- 
antorbital; Op, operculum; Pa. it, parieto-intertemporal; Po, postorbital; Pop. quj, preoperculo-quadratojugal; Ptr, postrostral; Sang, 
ang , supraangulo-angular; Scr, sclerotic plates; So, supraorbitals; Spl, splenial; Sq. pop, squamoso-preopercular; Stemp. ext , 
supratemporo-extrascapular; X, dermal bone-plate, probably corresponding to the dorsal part of the posterior end of the jugal 
of the Rhipidistia. 
similar processes are discernible at the bottom of the sinus in the dorsal margin, just behind 
the base of the antero-dorsal process. — A sensory canal (ifc) traverses the postorbital 
from the dorsal to the ventral margin in the way shown by text fig. 25 and PI. 5, fig. 2. 
The squamoso-preopercular (Sq. pop, text fig. 25; PL 5, figs. 2, 4; PI. 6, figs. 1, 2) 
is larger than both the preoperculo-quadratojugal and the postorbital. Its area is probably 
about three times as great as that of the latter bone. In shape it is somewhat irregularly 
four-sided. One can distinguish a posterior, an anterior, a dorsal and a ventral margin. 
The antero-ventral corner is much rounded and in other respects only slightly marked, 
the remaining corners are also rounded but are at the same time more pronounced, 
which is especially the case in reference to the postero-ventral one. The posterior margin 
is vertical, has a considerable height, and is slightly convex. Both the upper and lower 
margins are straight and converge towards the front, which makes the anterior margin 
9* 
