TRIASSIC FISHES FROM SPITZBERGEN 
24 
The development of the sphenoid clearly shows that the orbitotemporal region in 
Birgeria had definitely entered upon a development in the direction of the higher 
ganoids and Teleosts, although at the same time it preserved certain primitiva Crosso- 
pterygian-like characters. The latter characters consist especially in the presence of a 
single large ossification and the extension of this ossification basally behind the hypophysis. 
We do not know yet whether there were ossifications in the ethmoidal region. 
The membrane bones of the neurocranium. 
The parasphenoid seems in Palaeoniscids generally to have been large and well 
developed, and especially the part situated behind the ossification centre is sometimes 
characterized by a considerable width (Traquair 1877a; Fritsch 1895; Jaekel igo3; Day 
1915). This part is also at the same time rather short and probably did not as a rule extend 
backwards as far as to the posterior end of the neurocranium, while the anterior part 
reaches beneath the ethmoidal region. In the posterior part of the bone there issue on 
either lateral margin two processes, the anterior one of which is said to be furnished 
with a facet, against which the palatoquadrate would have articulated (Day 1915). The 
posterior process, which is always the most strongly developed, clearly corresponds 
to the processus ascendens in other ganoids. On the dorsal side of the bone there is 
sometimes described (Jaekel 1903; Day 1915) a fossa or a foramen that seems to have 
been related the hypophysis. 
In Birgeria the parasphenoid seems to be of a somewhat different type, a type 
resembling to some extent the usual actinopterygian one as it is found developed, for 
instance, in the sturgeons. It has extended posteriorly at least to the anterior part of 
the occipital region and is on the whole very wide and large. It has only the one 
processus developed on either lateral margin, and this which, is very broad and issues 
far from the posterior end in such a way as to cover the basipterygoid processes 
of its side from the outside. This fate is especially noteworthy as it shows that no 
articulation can have taken place between the basipterygoid process and the palato¬ 
quadrate. In the posterior end of the parasphenoid we find a deep longitudinal sinus, 
in which, according to the evidence of comparisons with the sturgeons, the arteria dorsalis 
was situated. No foramen or fossa related to the hypophysis is developed on the dorsal 
surface of the bone. On the other hand there issues from this surface on the part 
situated behind the ossification centre a paired ascending lamella, called by me the' 
profound lamella, which projects into the lateral wall of the primordial neurocranium, 
where it reaches high up posteriorly. 
The posterior portion of this lamella lies between the basioccipital and the prootico- 
opisthotic and is so situated that the labyrinth recess presumably reached to some 
extent in between it and the prootico-opisthotic, probably without coming into direct 
contact with the latter bone; except perhaps most ventrally the relations between the 
profound lamella and the cranial cavity cannot be established. 
In the profound lamella the parasphenoid has in Birgeria a very special character. 
It is possible that a similar lamella also exists in other Palaeoniscids, although so far 
it has not been found preserved. Nothing can as yet be said as to its morphological 
significance. 
Stensio, Triassic 
Fishes from Spitzbergen. 
