TRIASSIC FISHES FROM SPITZBERGEN 
211 
Of the genera so far known Boreosomus is undoubtedly most closely ^allied to the 
new genus Acrorliabdus found in the Triassic of Spitzbergen and described below. 
Boreosomus arcticus (A. S. Woodward). 
(Pi. 27, fig. 2). 
Synonyms: Acrolepis arctica, Woodward A. S., Upsala Geol. Inst., Bull., vol. XI, pp. 292—923, 1912. 
Aciolepis arctica? Stensio, E. A : son, Norske Geol. Tidskrift, vol. V, p. 77, 1918. 
Of this species, there are in the collections of the Palaeontological Institution of Upsala 
remains of six specimens (P. i 32 , P. i 36 , P. i 3 y, P. i 3 g, P. 695, P. 800) and in the Palae¬ 
ontological Collection of the University of Christiania a number of detached scales. Perhaps 
a specimen in the British Museum (B. M. P. 10929) may also be referred to this species. 
All the known specimens are fragmen- 
tarily preserved, and very little can be stated 
as to their general proportions. The length 
may however be estimated to about 35—40 cm. 
Visceral skeleton. 
The palatoquadrate is a triangular plate, 
which has its suborbital part low and its post¬ 
orbital one, on the contrary, high. One of 
its margins is directed ventrally, one antero- 
dorsally and one postero-dorsally. The antero- 
dorsal one is principally concave, the two 
others weakly convex. The anterior corner 
has presumably been rather pointed, but is 
not completely preserved. The posterior 
corner is prolonged downwards and the upper 
corner is truncated. 
The larger middle part of the palatoquadrate is situated rather sagitally. The 
anterior part is somewhat horizontal and the posterior part, corresponding about to the 
pars quadrata, is bent in a lateral direction. 
In the palatoquadrate there are two substitution bones, the autopalatine and the 
quadrato-metapterygoid. 
The autopalatine (Aup, text fig. 70) is a small flat bone situated, as usual, near the 
anterior end of the palatoquadrate. It consists of a cancelleous bone substance. 
The quadrato-metapterygoid ( Mplg . Q11, text, fig. 70) is a large and high bone. It 
occupies the most posterior part of the palatoquadrate cartilage and there is no doubt 
that it contains the homologues both of the quadrate and the metapterygoid, as is in¬ 
dicated by the name I have suggestet for it. No suture at all or any indication of a suture 
between the two components can be discovered, and it is certain that none has existed. 
The bone consists as a whole of cancelleous substance. It is exceedingly noteworthy 
that the metapterygoid component has on its anterior margin an antero-dorsally directed 
truncated process (pr), which may possibly have articulated with the basal part of 
the neurocranium in the caudal end of the orbitotemporal region. The position 
Text fig. 70. Boreosomus articus (a. s. Woodward). 
Palatoquadrate, mandibula and hyomandibular. 
After P. 137 Vi- 
Aup, autopalatine; Ecpt, ectopterygoid; Enpt, entopterygoid; 
Hm, hyomandibular; Mk, ossification in the Meckelian Carti¬ 
lage; Mptg. Qu, quadratometapterygoid; mg, fossa for mus- 
culus adductor mandibulae; pr, process from the meta¬ 
pterygoid component of the quadrato-metapterygoid, pos¬ 
sibly articulating with the neurocranium; pr.op, processus 
-ularis. 
