TRIASSIC FISHES FROM SPITZ BERGEN 
55 
otherwise composed of cartilage. Similarly the roof and floor of the same region seem 
to have been principally cartilaginous. 
On the prootico-opisthotic there can be distinguished a corpus and two processes, 
a dorsal one (fi) and a caudal one (c). The corpus is situated in the anterior basal half 
of the labyrinth region and is shaped like a four-sided pyramid, with the bluntly rounded 
point directed forward and somewhat medially, and the basal surface latero-caudally. 
Of its side-surfaces one is turned medially, one ventrally, one antero-laterally and one 
dorsally. Its anterior half consists of compact bone, its posterior part, on the other 
hand, is developed with a large cavity (lab. cay, text fig. 20), which is open both 
dorsally and caudally. 
The side-surfaces are really not very sharply marked off from one another, as 
the edges between them are rather rounded; this is chiefly the case with regard to 
antero-lateral and ventral ones. The medial one has an almost vertical position and is 
rather high posteriorly 1 ). Its posterior margin has a small sinus in its ventral part near 
the angle between itself and the posterior process (c) and it is conceivable that this 
sinus might have some connection with the exit for the nervus glossopharyngeus 
(IX? text fig. 19). The ventral side-surface (text fig. 23 ; PI. 7, fig. 2) is triangular, and 
its posterior margin has, besides the process c, a couple of smaller convex bends. Its 
medial margin is weakly and its lateral one rather strongly concave and the anterior 
corner is blunted. The antero-lateral side-surface (text figs. 19, 20) has an anterior part 
that is vertical and faces directly laterally and a posterior part that faces rostrally but 
at the same time somewhat dorsally as well. Its lower margin is concave, its posterior 
one convex, and its anterior corner is blunted. The upper one is convex in front of the 
process f h concave behind it, and the posterior upper corner projects upwards in the 
shape of a broad triangular part, which is covered by a process (li) from the dermal 
cranial roof. 
The cavity of the corpus of the prootico-opisthotic has the ossified walls (lateral, 
medial and ventral) thick and strong. Immediately in front of the cavity there issues 
on the dorsal side-surface of the corpus the process f t (text figs. 19, 20; PL 4, fig. 1; 
PI. 5, fig. 1; PI 8, fig. 1) which in the species under discussion is wide and powerful 
and almost or quite reaches the cranial roof. Close to its base there runs on the medial 
side a distinctly marked longitudinal furrow (sj, text fig. 20). The part of the dorsal 
side-surface of the corpus situated in front of the same process fj is convex from side 
to side and bluntly rounded at the front. 
The posterior process (c, text figs. 19, 20, 23 ; PI. 7, fig. 2) is sent out from the 
corpus at about the angle between the medial and ventral sides and is thus situated 
close to the supposed cranial base. As will be seen from the figures already given, it 
is fairly long and its breadth is also fairly considerable, whereas its height, on the 
other hand, is small. In Undina, as is clearly shown by a specimen in the British Museum 
(B. M. P. gi 3 o), by the original of Reis’s (1888) figs. 21 and 22, PI. 1, and also by 
Heineke’s (1907) type specimen of his fig. 1, PI. 6 and text fig. 1, the process in question 
is joined to the lateral surface of the basioccipital, which in this way becomes attached 
') Its characters are well displayed by the detached prootico-opisthotic figured on PI. 7, fig. 4. 
