40 
ERIK A : SON STENSIO 
Remarks. — The sculpture of the two best known of these four teeth shows a 
considerable resemblance to that of P. angustissimus and P. balatonicus. They differ from 
these two species by the distinct cone on the crown and a rather strong longitudinal 
keel. They differ distinctly from P. polaris both by their cone and their sculpture. 
The two other teeth are, as we have seen, too incompletely known to be charac¬ 
terized in detail, and I have included them here because they are the only ones found 
at the same horizons as the two preceding ones. 
It seems impossible as yet to decide whether’we are concerned here with a new 
species, as so far we scarcely know anything about the dentition of the palatoquadrate 
in P. polaris, and it also seems as if there were certain indications that this was some¬ 
what different from that of the mandible. We must consequently always take into 
account the possibility — even if it does not seen probable —• that the teeth described 
here could have belonged to the palatoquadrate in P. polaris. 
Geological occurrence and localities. — The teeth P. g6 and P. py were 
found at Mt Viking in the bone-bed 33 m above the fish horizon. 
The two teeth from Horn Sound belong to the material collected by Hoel and 
Rovig in 1917 and come from the north-eastern corner of this fjord, where they were 
collected about iom above the upper limit of the Carboniferous. 
Generically indeterminable fin-spines of Cestracionids. 
(PI. 1, figs. 12, 1 3 , 19.) 
In the present material of Elasmobranchii from the Triassic of Spitzbergen there 
are also fin-spines that differ in a number of respects from those of Hybodus and 
Acrodus. So far remains of three of these (P. 3 5, P. 4.3, P. 44) have been found, representing 
two different types. 
The best preserved of these fin-spines (P. 3 s; PI. 1, fig. 19) is the 
single representative of its type. In its present condition, with a 
part of the root and the point missing, it is 43 mm long, but its total 
length was probably at least 50 mm. The maximum width of the 
spine, from the anterior edge to the posterior surface, lies within 
the basal half and is about 8 mm. The maximum thickness from 
one lateral surface to the other lies immediately in front of the 
posterior surface and is approximately 4 mm. 
The fin-spine in question is only slightly arched backwards" It grows gradually 
and uniformly narrower distally and has apparently passed off in a rather sharp point. 
Its cross section is triangular (text fig. 16). The anterior edge is rounded, the postero¬ 
lateral edges are sharp, and the posterior surface is consequently well marked off from 
the lateral ones. All the surfaces are nearly plane. 
The anterior edge apart from that of the root is covered with a wide list of 
enamel, which also reaches out somewhat over the adjacent part of the lateral surfaces, 
in the way shown in PI. 1, fig. 19 b and text fig. 16. The exposed part of the lateral 
surfaces following caudally of this is furnished with rounded tubercles of enamel, 
arranged in rather distinct longitudinal rows. These rows, six or seven of which are 
P 
Text fig. 16. 
Cross section through 
fin-spine P. 35. 1/1. 
Thesection runsthrough the 
proximal end of the exposed 
part of the spine, e, enamel 
list on the anterior edge; 
p, pulp cavity. 
