2 3 4 
ERIK A : SON STENSIO 
concave, joins the postero-dorsal margin of the maxillary. The shape of the preoperculum 
in the whole bears a striking resemblance, as we shall see below, to that of the Catopterids. 
The operculum (Op, text fig. 76; PI. 3 o, fig. 1) is large and quadrangular in shape, 
with its shorter margins upwards (antero-dorsally) and downwards (postero-ventrally) 
and the longer ones forwards (antero-ventrally) and backwards (postero-dorsally) respec¬ 
tively. The upper, posterior and lower ones are weakly convex, the anterior one, on 
the other hand, is weakly concave. The posterior upper corner is well rounded, while 
the other corners are more or less well marked. 
The suboperculum (Sop, text fig. 76; PI. 3 o, fig. 1) is low but wide, the area of 
its surface being only about a third of that of the operculum. It has quandrangular 
shape but is especially low at its anterior end. Its anterior and upper margins are 
weakly concave and the posterior and,dower 
ones are weakly convex. The posterior lower 
corner is rounded; the other corners are 
well developed. 
The radii branchiostegi (Rbr, text fig. 76; 
PI. 3 o, fig. 1) are poorly preserved, and it 
is therefore impossible to establish their 
number with certainty. 
All the bones of the visceral skeleton 
described have a sculpture of fine striae, 
most often not particularly long, usually 
running parallel to the axis of length of the 
animal. More important deviations from this 
arrangement are only found on the ventral 
part of the operculum, where the striae run 
obliquely backwards and downwards. Other 
minor irregularities in the course of the 
striae do not disturb to any extent the 
impression of the horizontal arrangement of 
the sculpture. 
Dentition. 
The maxillary and dental are furnished on the labial margins with small pointedly 
conical teeth. Nothing else is known as to the character of the dentition. 
Skeleton of the shoulder girdle and the paired fins. 
Among the membrane bones belonging to the shoulder girdle we find remains 
of a high supracleithral ( Scl, PL 3 o, fig. 1) and a fragment of the cleithral (Cl, PI. 3 o, fig. 1), 
both of which have a sculpture of the same character as that of the opercular bones 
and the jaw-bones. 
The pectoral fins (Pc, PI. 3 i, fig. 1) are incompletley preserved. One can see, 
however, that some of their anterior lepidotrichia, probably as many as 7—8, were 
unjointed for some distance in their proximal part, and that the anterior margin of the 
Text fig. 76. Acrorhabdus asplundi n. sp. 
Parts of visceral skeleton. After P. 173. 3 / 4 . 
Ang, angular; De, dentalo-splenial; Mx, maxillary; Op, oper¬ 
culum; Po, p.reoperculum; Iibr, radii branchiostegi; Sop, sub¬ 
operculum ; orb , orbit. 
