TRIASSIC FISHES FROM SPITZBERGEN 
237 
the contrary, are jointed throughout their length, the joints being longer than wide. 
Ganoine sculpture in the form of fine longitudinal striae occurs on all the lepidotrichia. 
No fulcra are preserved. 
Nothing is known with regard to the ventral fins and the unpaired fins. 
Squamation. 
As far as is known, the scales (PI. 29, fig. 4) are mostly wider than high. As in the 
two other Acrorliabdus species, specially low scales are found on the ventral side and 
towards the back. Only in about the 5 or 6 most anterior vertical rows do we find 
behind the supracleithral and the dorsal part of the cleithral a number of scales with 
their height exceeding their width. Backwards, upwards and downwards on the body 
these scales gradually become lower. A few enlarged scales are found in front of the 
base of the pectoral fins. 
The anterior covered area of the scales was probably fairly wide, at least on those 
of the abdominal region. The conditions of the upper margin are not known, nor we 
know whether their posterior margin was entire or serrated. 
The sculpture on the present scales is on the whole rather strong. Immediately 
behind the shoulder girdle and at least on the anterior part of the back, however, it 
is considerably weaker than on the other known parts of the abdominal region. It con¬ 
sists of striation, and the striae are of two kinds, long ones traversing the exposed part 
of the lateral surface of each scale from the anterior to the posterior margin, and very 
short, always fine, ones occurring only along the posterior margin between the posterior 
ends of the former ones (PI. 3 o, figs. 3 —5). On the scales of the anterior vertical rows 
the long striae run rather obliquely in a backward and downward direction, then on 
the scales following backwards taking up such a position that they become nearly 
parallel to the upper and lower margins. On the scales present from the dorsum both 
the short and the long striae are fine (PI. 3 o, fig. 5) and, although the latter occur in com¬ 
paratively great numbers, the interstices between them are large. A similar fine 
sculpture is also present on those of the scales from the lateral surface of the abdo¬ 
minal region that follow in a couple of the vertical rows nearest to the shoulder girdle. 
On other scales belonging to the lateral surface of the abdominal region the sculpture 
is excedingly characteristic owing to a special development of the long striae (PI. 3 o, 
fig. 3 ). These, which are present to a number of from 4—8 according to the height of 
the scales, are rather narrow at the anterior ends but increase rather much in width 
backwards, finally at their posterior parts beginning to grow narrow again and becoming 
very much pointed close to their posterior ends. This narrowing towards the posterior 
ends always takes place rather suddenly, and the posterior fourths of the striae are con¬ 
sequently always separated from one another by rather large interstices, in which are 
found farthest posteriorly striae of the second kind. With regard to the long striae on 
the scales in question it is also noteworthy that they are flat and even, and that some¬ 
times two or three of the ventral ones on each scale may have their anterior ends bent 
upwards more or less parallel to the anterior margins of the scales. 
Towards the ventral side of the fish (PI. 3 o, fig. 4) the sculpture gradually changes 
so that all the longer striae become more uniformly narow, the interstices between their 
