210 
ERIK A : SON STENSIO 
The specimens so far found are from the following localities: Mt Congress, the 
South side of Sassen Bay, Mt Trident, Mt Milne Edwards and Mt Andersson. 
Genus Boreosomus n. g. 
Synonym: Acrolepis (in part) Woodward, A. S. Upsala Geol. Inst. vol. XI, 1912. 
The new genus for which I have suggested the name Boreosomus is characterized 
by the following features: Small or medium-sized fusiform fishes. The head with a 
sculpture of generally rather coarse longitudinal striae or somewhat lengthened tubercles. 
Mouth large. Hyomandibular oblique with a large processus opercularis. Branchiostegal 
rays few. Median jugular plate very large. Dentition probably rather weak, consisting 
on the margins of the jaws of fairly small acutely conical teeth, otherwise, at least 
partly, of small bluntly conical or almost spheroid teeth. Shoulder girdle sculptured 
in the same way as the head. The dorsal fin fairly weak, situated far forward, probably 
above or in front of the ventral fins. The caudal fin deeply cleft. The pectoral fins not 
especially strong. The ventral fins small and short-based. The lepidotrichia of the pectoral 
fins unjointed, at least in their proximal half; the lepidotrichia of the other fins densely 
.jointed throughout their length and situated close together. All the lepidotrichia are 
presumably more or less covered with ganoine. Fulcra are present, at least on the 
pectural fin, but are small. The scales on the most anterior part of the lateral surfaces 
of the abdominal region are higher than broad, gradually decreasing in height backwards, 
upwards and downwards, so that finally their width becomes greater than their height, 
Dorsally in each vertical row a number of the scales (10—20) are very low*. On the 
ventral side there are also low scales, but scarcely to the same extent as dorsally. 
Between the two ventral fins there are a few enlarged scales. Dorsal ridge-scales, at 
least in front of of the dorsal fin, slightly enlarged, but not prominent. All the scales 
are strong and thick, with the anterior covered area relatively wide. The antero-dorsal 
corner sometimes produced upwards. The dorsal margin with an articulatory spine, 
the posterior one serrated. The sculture of the scales immediately behind the shoulder 
girdle fine, otherwise consisting of a number of coarse, wide, densely placed ganoine 
striae, mainly running obliquely downward and backwards from in front and above. 
These striae, of which the ventral ones in certain species have their anterior ends bent 
upwards parallel to the anterior margin, are sometimes anastomized and extend as a 
rule quite over the exposed surface of the scales, ending with the posterior ends 
in the serrations of the posterior margin. Between their posterior ends short striae are 
inserted only on the most anterior flanc scales, but these short striae are never numerous 
and are always of the same or almost the same coarseness as the longer ones. 
Boreosomus closely resembles Acrolepis, especially in the development of the 
ornament of the scales, and Woodward’s view (1912, pp. 292—293) that the latter 
genus was represented in the Triassic of Spitzbergen is thus easily explainable. It 
is not yet possible to decide how close the relationship really is between them. It is 
evident, however, that Boreosomus differs from Acrolepis in the more forward position 
of the dorsal fin and the low shape of the scales towards the dorsum, and the small 
size of the dorsal ridge-scales. 
