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ERIK A : SON STENSIO 
The general shape of the head is the typical one for the Palaeoniscids, with the 
large orbital opening far forward. Nothing is known about the substitution bones of 
the primordial neurocranium. 
Membrane bones of the neurocranium. 
Nothing is preserved of the parasphenoid. The membrane bones of the cranial 
roof, on the other hand, are partly present on one specimen (P. 6yi c, PL 26, fig. 2), but 
they are so much broken that it is impossible to etablish their extension and mutual 
relations. Their sculpture consists of somewhat lengthened ganoine tubercles which run 
principally in the longitudinal direction of the head. They are placed transversally only 
over the middle part of the labyrinth region. 
Visceral skeleton. 
Nothing is known as yet with regard to the palatoquadrate and its bones. 
The maxillary {Mx, text fig. 69; PI. 25, fig. 3 ; PI. 26, figs. 1, 2) is of the ordinary 
Palaeoniscid type with a low subarbital and a high and long postorbital part. Its pos. 
tero-ventral corner is somewhat produced downwards, covering from the lateral side the 
posterior upper corner of the mandible. 
The mandible ( Md , text fig. 69; PI. 25, fig. 3 ; PI. 26, fig. 2) is well though not 
particularly strongly developed. Its anterior end is pointed. The coronoid process is 
lacking, as is usual in the Palaeoniscids. 
Of the bones of the opercular skeleton the preoperculum, operculum, suboperculum 
and a number of radii branchiostegi are present. 
The preoperculum (Po, text fig. 69, PI. 26, fig. 1; PI. 27, fig. 1) is incompletely 
preserved, but it is evident, however, that it has been an angular bone, whose ventral 
and narrower shank extended, downwards in the usual way between the maxilla on the 
one side and the operculum, suboperculum and most dorsal branchiostegal ray on the 
other. 1 ) Its dorsal and wider shank extended far forward over the cheek towards the 
orbit. From the whole position and shape of the bon we can certainly conclude that 
the hyomandibular was situated very obliquely, in the way that is characteristic of many 
Palaeoniscids. 
The operculum {Op, text fig. 69; PI. 26, figs. 1, 2; PI. 27, fig. 1) is a fairly large bone- 
plate, whose height is about double its width. From its position we can distinguish on 
it an anterior, a lower, a posterior and an upper margin. Of these the anterior one faces 
not only forward but also shomewhat downward, the posterior one not only backward 
but also somewhat upwards, and finally the lower one not only downward but also 
somewhat backward. The anterior margin is fairly straight or weakly concave and 
meets the lower one in a somewhat round and bluntly angular corner. The lower mar¬ 
gin is undulating in such a way that it is convex at the anterior and concave at the 
posterior part. The posterior margin, which is weakly convex, meets the lower one in 
an acute-angled corner. From the dorsal margin/which has also been weakly convex, 
it is not sharply marked off, as the corner between them is much rounded. The 
') Here as otherwise in the Actinopterygii I have described the preoperculum in connection with the 
visceral skeleton. 
