TRIASSIC FISHES FROM SPITZBERGEN 
261 
abruptly truncated. Finally it may be mentioned that the bone in question is pierced 
by the preopercular sensory canal. 
In this connection it ought to be noted that a preoperculum of a similar form has 
also been found in Colobodns .(Andersson 1916a Po, text fig. 2; PI. 1, figs. 1, 2; PI. II; 
Stolley 1920, PI. X, fig. 2; PI. XI, fig. 3 ; cf. also text figs. 85, 87 below). 
The operculum (Op, text fig. 81; PL 33 ; PI. 34, figs. 1, 2; PL 35, fig. 1) is a relatively 
small quadrangular plate with its width almost the same as its height. Its dorsal and 
posterior margins are nearly straight, or weakly convex, passing over into each other 
by a rounded corner. The anterior margin is concave and the lower one convex. It is 
impossible to decide whether the anterior upper corner was produced into a point 
extending forward into the angle between the posterior margin of the preo.perculum 
and the supratemporo-intertemporal or whether this part forms an in¬ 
dependent little bone-plate. The postero-ventral and antero-ventral corners 
are both angular but rather blunt and rounded off. 
The suboperculum (Sop, text fig. 81; Pl. 33 ; Pl. 34, figs. 1, 2; PL 35, 
fig. 1) is somewhat larger than the operculum. It is quadrangular in shape 
with its height considerably greater than its width. Of its margins the 
anterior one is weakly and the upper one strongly concave, while the 
lower and the posterior ones are both weakly convex. The anterior lower 
corner is almost right-angled, and the posterior lower one well rounded. 
The anterior upper and posterior upper ones are acute-angled. 
Both the operculum and the suboperculum thus show almost the 
same conditions as in Perleidus altolepis (cf. this work text fig. 78 B; 
Deecke 1888, PL 6, fig. 10; de Allessandri 1910, Pl. II, fig. 2). 
The radii branchiostegi (Rbr, text fig. 81; Pl. 33 ; Pl. 34, figs. 1, 2), of 
which those following immediately below the suboperculum were rather 
wide, seem to have been less numerous than in Colobodus. Their exact 
number could not be established. 
The external membrane bones of the jaws and the opercular 
hones are ornamented as a rule with densely arranged flattened tubercles 
in the same way as the membrane bones of the cranial roof. 
D entition. 
The dentition is rather robust compared with the size of the fish and consists partly 
•of pointed teeth and partly of teeth adapted for crushing. 
The premaxillary seems to have had only one row of large pointed teeth and 
similar teeth are also present in the anterior parts of the dentalo-splenial and maxillary. 
In a posterior direction, however, the teeth in these two latter bones soon become more 
blunt and more or less distinctly clubshaped (text figs. 81, 83 ), at the same time decreasing 
in height and increasing in thickness. Finally those farthest posteriorly which are situated 
close together get in profile the appearance shown in text fig. 83 B, Pl. 35, fig. 2, and in 
that shown in text fig. 83 C. 
Small teeth, probably mostly rather pointed, are found in a row laterally of the 
larger ones just described on the maxillary and dentalo-splenial. 
Text fig. 83. 
Perleidus 
woodwardi 
nom. nov. 
Teeth from the 
maxillary and 
dentalo-splenial. 
All magnified 
A) From the 
anterior part of 
the dentalo- 
splenial; After 
P. 185. 
B) From the 
posterior part of 
the maxillary in 
profile. After 
P. 186. 
C) From the 
posterior part of 
the maxillary in 
coronal aspect. 
After P. 1S6. 
The arrow in 
this figure 
points forwards. 
