TRIASSIC FISHES FROM SPITZBERGEN 
3 
said ought to be sufficient to. show the difficulties in dealing with Hybodus material 
consisting only of detached teeth. 
From the preceding it is clear that Jaekel already in 1889 had tried to undertake 
a partial revision of Hybodus as a genus. Nine years later (1898) he submitted the same 
genus as a whole to a closer investigation. He then suggests that the name Hybodus 
should be used only for fin-spines while the teeth should be divided among the genera 
Polyacrodus Jaekel, Orthybodus Jaekel, Nemacanthus Agassiz and Parhybodus Jaekel. 
Koken in 1907 justly objects that Jaekel has gone too far in his revision. He holds 
that H. reticulatus must be taken as the type species for the genus Hybodus, and that 
the name Hybodus must therefore not be restricted in the way maintained by Jaekel. 
Nor has Woodward followed Jaekel, but considers, like Koken, that H. reticulatus As the 
type species for Hybodus (1915, p. 4). Finally Schlosser (1918, p. 58) has adopted the 
g'enus Polyacrodus, though with a somewhat more restricted significance than Jaekel. 
Apart from this he retains in other respects the genus Hybodus as limited by Agassiz. 
The view I have arrived at myself with regard to this question and that I have applied 
in this work agrees fairly well with that of Schlosser. Like him, I consider, as will be 
seen from my exposition below, that we ought to restrict the genus Polyacrodus to 
teeth from the Triassic alone. It is beyond all doubt that the name Hybodus ought 
not to be used as Jaekel suggested and still seems to uphold in 1911b (p. 19). I am 
therefore quite in agreement with Koken/ and Woodward in considering the Jurassic 
species H. reticulatus as the type species for the genus Hybodus, so that this genus 
should comprise in the first place Jurassic and Wealden species. Our present knowledge 
of H. africanus seems to show that the species described from the Triassic ought, at 
least temporarily, to be also included in this genus. This seems perhaps to be contra¬ 
dicted by the fact, pointed out in the literature, that the Triassic species have a more 
heterodont dentition than the geologically younger ones. But with regard to this it 
must be remembered that even certain Jurassic species, e. g. H. delabechii, have teeth 
that have a rather different shape according to their position in the jaws (cf. Woodward, 
1888, pp. 58—60; 1889a, pp. 259^264). 
In the Triassic of Spitzbergen there occur Hybodus teeth together with those of 
Acrodus in various bone-beds. In the same bone-beds one also finds fin-spines, cephalic- 
spines and dermal denticles, a number of which probably belong to Hybodus. In no 
case, however, have I found them together .with teeth in such a way that their connection 
with these could be established, and I have described them in a special chapter after 
my accounts of the Hybodus and the Acrodus teeth. 
Finally in this connection it is worthy of mention that the Hybodus species from 
the Triassic of Spitzbergen seem to be closely related to certain of the species from 
the continental Triassic strata in Central Europe, while on the. other hand they seem 
to be more decidedly differentiated from the American ones. 
Hybodus rapax n. sp. 
(Pl.' i, figs. 1, 2.) 
Of this species there are only two detached teeth (P. 41 a , P.yi b) which are 
both defective.- 
