12 
ERIK A : SON STENSIO 
A tooth which, although considerably smaller (about 2 mm in length), is very 
like the one just described, occurs among the material from Horn Sound. 
The tooth P. 99 a (PI. fig. 2) is rather fragmentarily preserved and under these 
circumstances one cannot get any exact idea of its shape. In its present state of preser¬ 
vation it is about 5 mm long. 
The crown was almost straight with a somewhat powerful principal cone and 
prominent lateral cones. A longitudinal crista is developed as on the tooth before, but 
a transversal crista is here not only a distinguishing feature of the principal cone, but 
is also present on the lateral ones. Between each pair of the latter cristae there are 
one or two short striae, which do not reach as far as the longitudinal crista. 
The two teeth P. 99 b (PI. 2, fig. 3 ) and P. 99 c (PL 2, fig. 4) are also of a type 
similar to the one just described. The former differs somewhat, however, by being 
more bent and having smaller lateral cones. — With regard to a third tooth, P. 99 d, 
which also resembles in shape the teeth of the anterior transverse rows, it does not 
seem to be possible to decide with certainty, from the development of the crown 
(PI. 2, fig. 5), whether it belongs to Acrodus or Hybodus. But the root clearly indicates 
that the former alternative is the correct one. The principal cone of this tooth is 
certainly broken off, but all the same it is evident that it did not have a vertical 
position, but has been inclined somewhat towards the caudal end of the tooth. The 
sculpture of the crown is considerably finer than on that of the other teeth. 
An evident transition type between the anterior teeth and those following them 
farther posteriorly is seen in the tooth P. 99 e (PI. 2, fig. 6). This is 14 mm long and 
its greatest height is about 4 mm. Both the crown and the root, seen from the lateral 
and medial sides, are bent in the usual way, so that their dorsal contour is convex 
from one end to the other and the basal contour is concave to a corresponding degree. 
The bend is most evident from the lateral side (PI. 2, fig. 6 c). 
The principal cone is scarcely discernible here except as a marked angle above 
the middle of the tooth. Lateral cones are present but are very small. Seven can be 
observed on one side of the principal cone, six on the other. Between both ends 
of the crown extends the usual longitudinal crista, which, for the reason given immediately 
below, I call the primary longitudinal crista. On the principal cone there is, in addition, 
a well developed transversal crista. This is not ramified medially until near the basal 
margin of the crown, laterally, on the other hand, its ramification already begins at 
the place where it crosses the primary longitudinal crista and, as the ramification is 
abundant, the principal cone obtains a rather dense sculpture on this side (PI. 2, fig. 6 c). 
From the primary longitudinal crista there issues on the medial surface one or two 
sharp striae for each lateral cone; these striae pass off to or close to the basal margin 
of the crown. Between them appear other shorter ones, which are not connected to 
the primary longitudinal crista. On the lateral surface practically all the striae end in 
a similar way a short distance from the primary longitudinal crista, so that there arises 
a sculptureless surface close to this almost throughout the whole length of the tooth. 
On one half of the tooth — it is not possible to decide whether it is the posterior or 
the anterior one •— all the striae of the lateral surface have their distal ends curved 
in the direction of the principal cone and are then attached to each other, so that a 
