TRIASSIC FISHES FROM SPITZBERGEN 
27 
Remarks. Of the fin-spines mentioned here P. 102, P. 282 and P. 883 belong 
undoubtedly to the Hybodus and Acrodus type; P. 42 differs by having a partly diverg¬ 
ing microscopic structure, but it is not yet possible to ascertain the importance of 
this. It is of course also conceivable that P. 42 showed different conditions with regard 
to sculpture, etc. from the typical spines. But, at least for the present, I thought I 
could group it together with them. 
The fin-spine P. 282 seems to resemble rather much the spine described by Jaekel 
under the name of Hybodus laczkoi (Jaekel, 1911b, p. 18, text fig. 7), but it is curved in 
another way. It is well differentiated from H. dimidiatus by its general shape and the 
appearance of the denticles (cf. Jaekel, 1889). 
The other fin-spines are too incompletely known to be compared with the ones 
described earlier. 
Geological occurrence and localities. — The fin-spine P. 282 was found on 
the east side of Mt Marmier in a bone-bed in the fish-horizon; the fin-spine P.42 was 
found at Mt Viking in the bone-bed 33 m above the fish-horizon. The two other fin- 
spines belong to the material collected by Dr. B. Hogbom and the locality is given on 
the labels only as «Middelhook». P. 883 was found 
some metres below the lower Saurian level and 
P. 102 in the «Daonella layers*, i. e. in or near 
the upper Saurian horizon. 
Dermal denticles. 
Detached dermal denticles are present in great 
numbers and it seems certain that at least a part 
of them belonged to Hybodus and Acrodus. Certain 
of them even resemble those described by me above in A. oppenheimeri (p. 24). 
Others, as'Pl. 1, fig. 14 and text figs. 11 A, B, C show, have partly another appearance. 
Text fig. II. Dermal denticles. 
A, from P. 57«/ i; B, from P. 77"A; C, from 
P. 609 6 /,. 
Geological occurrence and localities. — Detached dermal denticles are 
found in all bone-beds. In two of these, namely the one 33 m above the fish-horizon 
and the one in the lower Saurian horizon, they are exceedingly common. The one in 
PI. i, fig. 14 and the two in text figs, n A and C come from the former horizon, while 
the one in text fig. 11 B comes from the latter. 
Genus Polyacrodus Jaekel. 
Synonym: Hybodus (in part) Jaekel, 1889. 
The genus Polyacrodus was founded by Jaekel in 1889 (p. 32 1) for certain teeth 
from the Triassic, which were considered by Agassiz and subsequent authors to belong 
to Hybodus. Jaekel’s characterization of the genus at that time can be summarized as 
follows: The teeth agree with Acrodus with regard to the root. The crown in its general 
development is like that of Hybodus, with a principal cone and lateral cones, but all 
these cones, unlike those of Hybodus , have a short skittle-like shape. The crown has a 
longitudinal keel. The striae issuing from this on both sides and passing off fairly trans- 
