ERIK A : SON STENSIO 
IO 
A. oppenheimeri, one of the newly-established species, resembles in certain respects the 
tooth-type from the continental Triassic of Europe which is called A. gaillardoti Agassiz, 
while A. spitzbergensis and the other species seem to resemble more closely the North 
American forms. 
As has been 'pointed out above in the introductory description of the genus 
Hybodus (p. 3 ), fin-spines, cephalic spines and dermal denticles of this genus and of 
Acrodus are often found detached in the same horizons as the teeth. But these conditions 
of occurrence of the spines and dermal denticles do not of course permit of any decision 
as to which of them ought to be referred to Acrodus or Hybodus, since, as we know 
(Day, 1864; Woodward, 1889 a; Jaekel, 1889), they are similarly developed in both these 
genera. Because of this I have described them all below in a special chapter (p. 25). 
Acrodus spitzbergensis Hulke. 
(PI. 2, figs. 1—19.) 
Syn. 1873. Acrodus spitzbergensis Hulke, I.W., Stockholm K. Yet. Akad. Handl. Bih., Bd. 1, no. 9, p. 10. 
1889. Acrodus spitzbergensis Woodward, A. S., Catalogue of Fossil Fishes in the B. M., Part I, p. 299. 
1918. Acrodus spitzbergensis? Stensio, E. A : Son, Norsk Geol. Tidskrift, Bd. Y, pp. 76—77. 
In the material of the Triassic vertebrates collected by A. E. Nordenskiold during 
the Spitzbergen expedition of 1864 Hulke (1873, p. 10) was able to recognize a tooth 
of an Acrodus species also, which he described under the name of A. spitzbergensis. His 
description is as follows in extenso: «A single, but characteristic tooth o - g inch long 
and having a greatest breadth of not more than 0-12 inch, imbedded in a thin piece 
of limestone labelled (95 Is fj. 1864, Saurie Hk.) plainly belonged to an Acrodus. The 
striae rather coarse, and separated by proportionately wide intervals, pass off from the 
lips of a sunken groove instead of from a raised line as in all hitherto known species. 
I am indebted to Mr. Davies, Senior, for calling my attention to this distinguishing 
character, and a comparison which I made of this spitzbergen fossil with a large series 
of acrodus teeth in the British Museum, has confirmed its distinctiveness.* The tooth 
in question belongs to the State Museum in Stockholm, but could not be found, having 
either got lost or being missing at the time. 
The material of this species now available shows that the distinguishing character 
of the type tooth, the longitudinal groove from whose raised lateral «lips» the striae 
issue, is as a rule only found on the teeth of the posterior and median transverse rows 
of each jaw. Those of the anterior transverse rows are developed, as we shall see, 
with a number of cones and sometimes have a decided resemblance to those of Hybodus. 
I have provisionally grouped under the name of A. spitzbergensis about 20 detached 
teeth from the Ice Fjord district (P. 98 a — m, P. 99 a — e, P. 100), all belonging to the Palae¬ 
ontological Institute of Upsala. I have previously described with some hesitation a number 
of teeth from Horn Sound under the same species name (Stensio, 1918 b), and the view 
I put forward then has been confirmed on the whole, at least by the facts known up 
to the present. The teeth from Horn Sound, which I shall deal with again here, belong 
to the Palaeontological Collection of the University of Christiania. 
Teeth of the anterior transverse rows. — The transition between the teeth 
of the anterior and middle transverse rows of each jaw apparently takes place gradually, 
