3o 
ERIK A : SON STENSIO 
as in the preceding type. The curvature is strongest on the side I take to be the lateral one 
(text fig. 12D; PI. 1, fig. 23 c). Above or . in the neighbourhood of the middle of the 
crown there is a principal cone, certainly rather low but all the same quite prominent, 
and on both sides of this there is towards each end a very blunt and low lateral cone 
in the way shown by the figures. The principal cone often has a markedly pyramidal 
shape and is in a characteristic way considerably wider from the lateral to the medial 
side than the crown is otherwise, so that, seen from the distal end, it appears as a distinct 
thickening at the middle of the crown (PL 1, fig. 23 a). This thickening is strongest on 
the side that I take to be the lateral one (text fig. 12D; PI. 1, fig. 23 c), where it con¬ 
tinues in a basal direction right to the basal margin of the crown. 
The two ends of the crown are rather high and rounded. Between them a median 
longitudinal keel extends over all the cones. The surface of the crown both laterally 
and medially of this keel is divided lengthways into a dorsal and a basal half, the 
former of which faces dorso-medially, the latter ventro-medially. The two halves meet 
in a not very prominent longitudinal edge (text 
figs. 12 C, D). The whole appearance seems to me to 
indicate that a notch was developed here between 
the root and the crownboth on the medial and the 
lateral side. 
The sculpture is most developed on the lateral 
side and closely resembles that described on the two 
teeth P.yi^a and P.yiya. The striae are, however, 
considerably shorter (text fig. 12D). On the medial 
side the sculpture is limited to the principal cone and 
consists of a few rather coarse striae. Both on the medial and the lateral side the 
striae of the principal cone exhibit a slight convergence in distal direction. 
Of a third type of teeth the present material contains only two crowns, P. 712 b 
and P.716CI (text fig. 12E; PI. 1, figs. 24, 25). The larger of these (P.yi2b) has been 
about 8 mm long and its maximum height has been 3 mm; for the other the same mea¬ 
surements amount to 6mm and 2'5mm respectively. Both teeth are bent in the same 
way as the preceding ones and also show with regard to their shape some obvious 
resemblances to them. They have a strong and broad but bluntly rounded principal cone. 
One of them, P. 716a (text fig. 12 E, PI. 1, fig. 24), has on each side of the principal cone only 
one lateral cone, while the other, on the contrary, seems to have had two. The deve¬ 
lopment and position of the lateral cones is the same as on the teeth belonging to the 
type described just above. As in these, so here too the principal cone is thicker than 
the rest on the tooth. The thickening on the medial side is, however, still more marked 
in this type and its continuation in the basal direction even forms a distinct swelling 
on the basal margin. 
A notch between the root and the crown has been developed at least on the 
medial side. 
The sculpture is nearly quite lacking, but if this is due to weathering or ought to 
be considered as a primary condition cannot be decided. As far as one can see it consists 
only of some indistinct striae on the principal cone. 
Text fig. 12. 
Polyacrodus pyramidalis n. sp. 
Teeth of the three types present. A, B‘, from 
P. 717a. and P. 714a respectively; C, D, from 
P. 7/5 a and P. 715 b respectively; E, from 
P. 716 a. All teeth with magnification 4/1. 
