252 
ERIK A: SON STENSIO 
As far as can be judged the lepidotrichia are without ganoine covering and are 
unjointed for a short distance at their proximal ends. Otherwise they seem to have been 
densely jointed. The joints vary somewhat in shape. Thus sometimes they are wider 
than long, sometimes, on the other hand, they are somewhat longer than wide. 
The scales (PI. 27, fig'. 4; PI. 28, fig, 2; PI. 32 , fig. 1) are of the usual type characteristic ' 
of the Platysomids. The dorsal margin has close to the anterior end a well developed, 
sharply marked off articulatory spine. The anterior covered area of the lateral surface 
is fairly narrow, as it ought to be in Platysomns. On the medial side there is close to 
the anterior margin a well marked rounded ridge, whose upper end extends into the 
above mentioned articulatory process on the dorsal margin (PI. 28, fig. 2), It is note¬ 
worthy that the ridge is widest and most robust at its middle parts. Just behind the 
ventral part of this ridge we find, at least on certain scales, the usual articulatory fossa. 
The posterior lower corner on all the scales has an obtuse angle. The anterior lower 
and posterior upper ones are most often acute-angled, but may also in certain cases be 
almost right-angled. The posterior margin is straight and not denticulated. 
The sculpture of the scales (PI. 32 , fig. 1) consists of a number of extremely fine 
striae lying close together and running from above downwards ond somewhat forwards. 
As a rule they are weakly undulating but may also at a number of places make more 
abrupt curves and exhibit some irregularities in the arrangement. On certain scales a few 
striae are also found directed along the upper and lower margins, while the great majority 
are in the normal position. 
Remarks. — This species is well characterized both by its considerable size and 
the sculpture of its scales. I have named it after the late Professor A. G. Nathorst, 
whose contributions to the investigation of the geology of Spitzbergen are too well 
known to make it necessary for me to give any detailed reasons for this step. 
Geological occurence and localities. — Specimens P. 141 and P. 142 come from 
the fish horizon at Mt Trident. The detached scales (P. 2o3, P. 692, P. 6 g 3 , P. 8yg), 
that I have hesitatingly included here, come partly from the fish horizon, partly from . 
strata immediately below that. The localities were Mt Trident, Sticky Keep and 
Mt Marmier. 
Platysomus sp. 
Under this heading I place only one specimen (P. 140), which is poorly preserved 
and incomplete on the whole. In its present state of preservation it measures about 
16 cm in length without head and caudal fin. One might venture to estimate the total 
length at close on 25 cm. As far as can be seen the greatest height is about ncm and 
the fish has thus the general shape characteristic of the Platysomids. 
The dorsal fin is very long and consists of a large number of lepidotrichia, but 
no details as to the nature of these can be given. Some of the ossifield middle segments 
(baseots) of the endoskeletal radials are preserved. They are rather short and somewhat 
hour-glass-shaped. Nothing can be established as to their number in. relation to the 
lepidotrichia. 
