ERIK A : SON STENSIO 
Dentition. 
The dentition in . 4 . robusta is, in its general character, typically adapted for crushing. 
The parasphenoid, the pterygoid, the intercoronoideo-prearticular, the coronoid and the 
membrane bones on the copula are furnished with spheroidal flat teeth which are largest 
and strongest on the parasphenoid and the membrane bones on the copula, smallest on 
the intercoronoideo-prearticular. On the last-mentioned bone they are also mainly 
confined to the dorsal parts. Their distribution on the parasphenoid is seen in text fig. 42 
and PI. 16, fig. 1 and on the pterygoid in text fig. 47. 
The dentition of the precoronoids, maxillary and premaxillary is unknown. 
The branchial arches were, as far as one can judge, furnished with small teeth- 
bearing plates. Large numbers of such plates are often seen, scattered among the 
different parts of the visceral skeleton. The teeth on these plates, the majority ol which 
are small, are sometimes conically pointed, sometimes, and that is probably most general, 
they are blunt or spheroidal. The small plates which Reis (1888, pp. 47, 51; PI. II, fig. 2) 
has described in the Jurassic forms as «Sclerotical- 
pflaster» were probably tooth-bearing plates belong¬ 
ing to the branchial arches. 
As far as one can see, the pointed conical teeth 
are smooth. The spheroidal ones, on the contrary, 
have a fine striation radiating from a centrally 
placed, wart-shaped little protuberance (PL 16, fig. 2); 
in this way they strongly remind one of the typical 
spheroidal Colobodus- teeth. Their agreement with the 
latter, as I have pointed out in an earlier work 
(Andersson, 1916 a, pp. 27—28) is so great that if one 
met with them detached one would consider them 
undoubtedly as pertaining to Colobodus. 
The sensory canals of the head. 
The sensory canals of the. head were strongly developed and opened outward with 
large, generally oval pores. In the cranial roof and the mandibula they are preserved 
almost completely. In the cheek they are found in a more fragmentary condition, but 
their course is also there partly well shown. 
The anterior end of the supraorbital canal (text figs. 43, 44) is situated in the most 
lateral one of the rostral plates, a little antero-ventrally of the anterior nasal aperture. 
From here it rises in an arch upwards and backwards, enters the nasalo-antorbital 
dorsally of the nasal capsule, runs through the whole length of that bone and then 
between the supraorbitals and the fronto-dermosphenotic, till at last in the postero-lateral 
part of the latter bone it anastomoses with the infraorbital canal. If this anastomosis ' 
was formed with its posterior end or whether this end continued in a posterior direction 
medially of the infraorbital canal as an anterior head line of pit organs it is not possible ' 
to say. In the part of the canal situated between the supraorbitals and the fronto- 
dermosphenotic three large oval pores are found (p, text figs. 39,40,43, 44; PI. 14, figs. 1—2.) 
It is also evident that one or more pores of a similar kind must have been developed 
Pterygoid with dentition. 
From P. 'iSy. P. iSg and P. ig 5 . 3 /„. 
