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ERIK A : SON STENSIO 
posterior ends being decreased in width but at the same time extended more forward. 
The scales on the ventral side seem, with regard to their sculpture, scarcely to differ 
from the correspondingly situated ones in Acrorhabdus bertili. A difference may, however, 
possibly exist in the number of the longer striae being somewhat greater in A. bertili 
than in the species in question here. 
* * 
Remarks. — Acrorhabdus latistriatus is characterized especially by its partly unique 
scale sculpture and is clearly separated by this both from Acrorhabdus bertili and Acrorhabdus 
asplundi. As has also been shown by the account given above, it further differs from 
these two species by a somewhat different shape in certain of the bones of the head. 
The scales on the ventral parts in the species under discussion and those in 
Acrorhabdus bertili are so similar that it is impossible to distinguish them with certainty 
when they occur detached. 
The species name latistriatus refers to the character of the striation of the scales 
belonging to the lateral surfaces of the abdominal region. 
Geological occurrence and locality. — Acrorhabdus latistriatus is so far only 
known from the fish horizon at Mt Andersson. 
The organisation of the Palaeoniscids. Summary. 
It is not my intention in this connection to give a complete account of the 
organisation of the Palaeoniscids, but I shall confine myself chiefly to a summary of the 
most important results afforded by the Spitzbergen material. In connection with this, 
however, it has also been necessary to give a summary of a number of scattered 
observations published during recent years with regard to the osteology or the Palae¬ 
oniscids. 
The primordial neurocranium and its ossifications. 
The primordial neurocranium in Birgeria is, as we have seen, low and broad. In 
the great majority of the Palaeoniscids, on the other hand, to judge from the general 
orm of the head, it cannot have shown the same conditions, but must have been higher 
fand narrower. The snout is always prolonged to some extent and forms a short rostrum. 
The dorsal surface slopes down rather gently and uniformly forward. The basal surface 
is only known in any detail in Birgeria, where, seen in profile, it is somewhat convex 
under the anterior part of the orbitotemporal region, becoming concave posteriorly under 
the posterior part of this region and the anterior part of the labyrinth region. The 
greatest height of the primordial neurocranium is in Birgeria in the middle or posterior 
part of the labyrinth region. 
In the majority of Palaeoniscids the ethmoidal region is high and, in spite of the 
rostral prolongation, short. No further details are know about it. The orbitotemporal 
region forms a wide interorbital wall between the large orbits and the cranial cavity 
has continued through the whole length of this region. Posteriorly the orbitotemporal 
region passes without any sharp boundary into the labyrinth region and at least in 
certain forms (Birgeria) its ventral part may be pierced by a small fenestration so situated 
that it partly corresponds to the fenestra optica of the Teleosts. As is usual in fishes, 
