TRIASSIC FISHES FROM SPITZBERGEN 
199 
An attempt to modify somewhat the contradiction that has arisen between this 
theory and the more recent theory advocated by Palaeontology has been made by Abel, 
as he points out that the theory of the lateral fold must perhaps be considered 
applicable to such forms as the Acanthodes (1919, pp. u 3 , 147, 148). But in my opinion 
it is open to question whether these, like the Actmopterygii , were not adapted to a nectonic 
mode of life and whether under such circumstances a transformation of their paired fins 
did not take place. 
Squamation. 
The squamation was almost entirely reduced. As in Phanerosteon (Traquair, i 9 i i a, 
pp. 165—166, text fig. 9; Fritsch, 1895, pp. 98—94, text fig. 287), Elpisopholis (Woodward, 
1908 a, p. 17) and Psilichtliys (Hall 1900, p. 148), scales were present only on the dorsal 
lobe of the caudal fin. These scales (PI. 24, fig. 1) are high and narrow and are arranged 
in the way that is characteristic for the Palaeoniscids. The evidence seems to show that 
they are without ganoine covering. 
Main lateral line of the body. 
The lateral line of the body (/, PI. 21, fig. 4) was enclosed in small, narrow tubes of 
bone, arranged in a series one after the other. In the caudal fin the lateral line passes 
off, as in the sturgeons, along the lower margin of the dorsal lobe, quite close to the 
bases of the lepidotrichia. 
# 
Remarks. — I consider that I have established with certainty that the remains 
described here as Birgeria mougeoti belong to the same genus as the species adopted 
by Agassiz under the name of Saurichthys mougeoti. 
The determination as to species, on the other hand, can only be regarded as 
provisional, as it is based almost exclusively on the teeth. Nor'was it possible to decide 
with certainty whether the material present represents one or two closely related species. 
Geological occurrence and localities. — Detached teeth of the Birgeria 
mougeoti type occur in the bone-bed found by Salomon in the lower Triassic, in a bone- 
bed in the fish horizon and in the bone-bed 33 m above this horizon. The other remains 
all originate from the fish horizon. 
The localities of the finds were as follows: Mt. Congress, Mt. Marmier, Mt. Viking, 
Sticky Keep, Mt. Trident, Mt. Milne Edwards and Mt. Andersson. 
Birgeria sp. 
(PI. 24, fig. 3 .) 
Under this heading I have placed a number of detached teeth from a bone-bed in 
the upper Triassic (P. 712 — P. 718). The teeth in question are all incompletely preserved, 
their basal parts being always more or less absent. In addition they often seem to be 
somewhat worn. 
They are rather small and slender and generally have a rather long and strikingly 
pointed enamel cap (PI. 24, fig. 3 ).' In most cases this enamel cap has a sculpture of 
