18 6 
ERIK A : SON STENSIO 
but hardly anything was known as to the conditions of its different elements. From the 
description given by me above we see, however, that the skeleton of the branchial 
arches can as a whole be looked upon as typically Actinopterygian-like. Among the 
recent Actinopterygii, B. mougeoti seems, at least with regard to the ossifications in the 
branchial arches and copulae, to approach most closely to Amia and the Teleosts. 
Dentition. 
All the teeth are more or less pointedly conical in shape. 
The labial border of the maxillary and dental are furnished with two rows of 
teeth, a medial row of large powerful ones and a lateral row with considerably smaller 
ones. The teeth situated nearest to the lateral margin of the ectopterygoid and on the 
upper margin of the mixicoronoid are of about the same order of magnitude as those 
in the lateral row of the maxilla. The ectopterygoid and the mixicoronoid together 
with the entopterygoid are, in addition, densely provided on their medial surfaces with 
strikingly small teeth. The conditions of the dentition on the parasphenoid and the 
premaxilla are unknown. The branchial arches had numerous fine and relatively 
long teeth. 
On the smallest teeth (e. g. the majority of those belonging to the pterygoid and 
the mixicoronoid) only few details can be observed. As a rule, however, it is possible 
to verify that the pulp cavity was present and the point was covered with a cap of enamel. 
The largest teeth present (P. 5^5) are about 15 mm high with their distal part not 
infrequently bent a little like a thorn towards the medial side. They seem to resemble 
most the shape of tooth that Munster (i 83 g, p. 119) and Agassiz (1844, vol. II, part 2, p. 87) 
have distinguished under the name of Saurichthys semicostatus, but which Woodward 
(1895 b, p. 20) and previously v. Meyer (1849 b, p. 235) and Eck (1865, p. 120) adopted as 
a synonym of Sauriclitfiys mougeoti, i. e. of Birgeria mougeoti. The enamel cap that covers 
the point is 1 / s — 1 / 4 of the total length of the teeth and is divided into a medial and a 
lateral half by a sharp edge placed sagittally. This cap is also furnished with a sculpture 
of some raised and fairly sharp striae (Pl. 21, figs. 5, 6), placed sparsely and generally 
developed in about the same way on both sides of the sagittal edge. If these are sometimes 
weaker on one side, then it always seems to be the medial side. They proceed from the 
basal edge of the enamel cap and extend distally to about the middle of its height or 
slightly farther. The remainder of the cap is therefore smooth. With regard to the 
striae it may further be added that they are often not quite straight but somewhat 
undulating, and that generally they are of rather different height on the same tooth. 
A macroscopic investigation of the big teeth shows clearly that the enamel is not 
restricted to the cap alone but that it continues from there towards the bases of the 
teeth as a thin covering. This covering can be seen extending about to the boundary 
between the middle and proximal thirds of the total heights of teeth but is exceedingly 
thin nearest this place. 
The larger teeth from the fish horizon (PI. 21, fig. 5) all seem to have had the 
enamel-covered part furnished, basally of the real enamel cap, with a very fine vertical 
striation. The same conditions are also shown by a number of larger teeth (PI. 21, fig. 6) 
found in the bone-bed 33 m above the fish horizon at Mt Viking, while others from 
