32 
ERIK A : SON STENSIO 
an angular swelling. The side accessible for investigation — appearently the medial one 
— is divided lengthways by means of a blunt longitudinal edge into a basal and a 
distal longitudinal part about in the same way as in P. pyramidalis. 
A median longitudinal keel seems to have been present. A transversal keel is 
developed from the distal end of the principal cone to the longitudinal edge of the 
medial side. Otherwise the medial side is quite without sculpture. 
The crown has been wider than the root and between them there has been a 
notch at least on the medial side. 
The third known type of teeth is represented by three crowns, all of which are 
bent in the usual way in the vertical plane through the axis of length. In this case, 
however, the curvature is fairly strong (text fig. i 3 C; PL i, fig. 27). There is no real 
principal cone, although the crown has a very distinct angle and is strongly thickened 
at the place for this cone on the lateral side. Lateral cones, on the other hand, are 
indicated on one of the crowns and corresponding to each of them 
there is a thickening on the lateral side. 
A median longitudinal keel is present and there seems to be 
also a transversal keel over the highest part of the crown, at least 
on the medial side. This side, which is without any other sculpture, 
is developed in the same way as in the type just previously de¬ 
scribed (cf. text figs. 1 3 B and C). The lateral side has also been 
smooth. The crown has been wider than the root and a notch was 
formed between them, at least medially. 
With regard to the microscopic structure P. angulatus agrees with P. pyramidalis. 
Text fig. 13. 
Polyacrodus angu- 
latus n. sp. 
Three types of dental 
Remarks. — I am of the opinion that the three types of teeth described here 
ought to be grouped under a common species name, as, in spite of a large number of 
differences, they still have important features in common. 
Polyacrodus angulatus seems undoubtedly to be rather closely related to P. pyramidalis. 
It differs from this, inter alia, by a different development of the cones, the almost total 
absence of striation, and probably also by its smaller size. 
It is also noteworthy in this connection that P. angulatus resembles to a rather great 
extent certain of the types of teeth that have been incorporated with Acrodus minimus 
Agassiz. This is true, for instance, of the teeth described by Agassiz (1843, vol. Ill, 
p. 146; PL 22, figs. i 3 —15) under the name of Acrodus acutus and also Plieninger’s (1844, 
p. 116; Pl. X, figs. 20—22, 27) so-called Thectodus species. Whether the resemblance ex¬ 
tends further than the exterior is, however, not known, but this would certainly be 
worth further investigation. 
The name angulatus for this species refers to the fact that the tooth crowns have 
not infrequently an angle developed in the highest part. 
Geological occurrence and locality. — P. angulatus is so far known only 
from the bone-bed found by Salomon in the lower Triassic at Mt Congress, where it 
seems to be rather common. 
