42 
ERIK A : SON STENSIO 
layer (d). It is probable that, at least at its most central part, this consisted of ortho¬ 
dentine. Outside the more compact layer the trabecular-dentine follows in the usual 
way, and text fig. 17 shows that this was developed especially thickly in front of the 
pulp cavity. 
Remarks. — The fin-spine P. S5 closely resembles both Nemacanthus (cf. Wood¬ 
ward, 1891b, pp. 115 — 117; Jaekel, 1892, pp. 145—151; etc.) and certain of the spines 
described under the generic names Cosmacanthus and Geisacanthus (Davis, i 883, 
pp. 355—358; St. John and Worthen, 1875, pp. 440—442; Woodward, 1891b, pp. 111 — ii 3 ; 
Evans, 1904, pp. 397—402). Until it has been decided whether denticles were present in 
its posterior surface or not its relations will, however, remain very uncertain. 
The two fin-spines P. 43 and P. 44 seem to belong to a rather special type, but 
they are not sufficiently well preserved to be fully compared with previously known types. 
If one might venture to express a supposition as to the teeth to which the fin- 
spines described here belong, it looks most probable that these are Polyacrodus and 
Palaeobates. 
Geological occurrence and locality. — All three fin-spines (P. 35, P. 43 and 
P. 44) come from Mt Viking, where they were found in the bone-bed 33 m above the 
fish horizon. 
Subclass Teleostomi. 
Order Dipnoi. 
Genus Ceratodus Agassiz. 
Ceratodus sp. 
(PL 3, fig. 19.) 
The material hitherto discovered consists of a right mandibular tooth (P. 350), on 
which the lateral part with the processes is broken off (PI. 3 , figs. 19 a—d). The tooth 
is still connected basally with a piece of the so-called splenial (Spl, text fig. 18). 
It seems to have agreed very well in size with the mandibular teeth in C. sturii 
Teller (1891, pp. 22 — 3 i; PI. Ill, figs. 3 —6; PL IV, fig. 4). It has had the usual triangular 
shape, and its medial and caudal borders meet at a marked angle, the so-called angulus 
internus. 
As in C. sturii and C. kaupii (Stromer and Peyer, 1917) the medial part of the 
masticatory surface is fairly plane. Laterally of this three distinct ridges gradually 
rise. A fourth, farthest posteriorly, is only slightly indicated. The first and the third 
have their axes of length converging towards a point situated just antero-medially of 
the angulus internus. The axis of length through the second runs so that the medial 
prolongation passes some distance behind the angulus internus. The fourth ridge is 
situated close to the caudal margin of the tooth and runs about parallel to the third. 
The groove between the first and second ridge is in the usual way wider than that 
