236 
ERIK A : SON STENSIO 
The preoperculum ( Po , text fig - . 77; PI. 29, fig. 4) is, as in Acrorhabdus asplundi, a 
large triangular plate, but is wider than in this species. Its posterior margin is convex, 
the two other margins are probably concave. 
The operculum (Op, text fig. 77; PL 29, fig. 4) apparently had a similar shape to 
the one in Acrorhabdus asplundi, but it is strikingly higher and has a more vertical 
position than in this species. Its anterior margin is strongly concave, while the three 
others are weakly convex. Of the latter the dorsal and caudal ones pass over into each 
other without any definitive boundary, as the postero-dorsal corner is well rounded. The 
other corners are well pronounced, and especially noteworthy is that the anterior lower 
one is here obtuse-angled, while in Acrorhabdus asplundi, on the other hand, it is almost 
right-angled. 
The suboperculum (Sop, text. fig. 77; PL 29, fig. 4) is low and very small compared 
with the operculum. It is only a little larger than the branchiostegal radii following 
ventrally of it. Its shape is quadrangular, being somewhat higher posteriorly than ante¬ 
riorly, but not so much as in Acrorhabdus asplundi. As 
in this species, its anterior and upper margins are weakly 
concave and its posterior and lower ones weakly convex. All 
four corners are rounded and the postero-dorsal one is con¬ 
siderably more blunt than in Acrorhabdus asplundi. 
The branchiostegal radii (Rbr, Pl. 29, fi g. 4) are very few; 
their number was probably not above five. Except for the 
dorsal one they are all incompletely preserved. 
The median jugular plate (Mg, Pl. 29, fig. 4) is also 
certainly incomplete too, but it is undoubtedly clear that it 
was of about the same size as in Boreosomus reuterskioldi 
(cf. text. fig. 71; Pl. 28, fig. 1). 
The sculpture on the above-described bones consists 
mostly of fine, rather short, sparse striae, principally running 
in the longitudinal direction of the animal. Along the labial margin of the maxillary 
and dentalo-splenial the striae are replaced by comparatively small, round tubercles, 
lying close together. On the median jugular plate a number of median striae pass off 
in the usual way in a longitudinal direction, but on each side of these on the lateral 
parts of the plate the striae are arranged so that they run in a postero-lateral direction, 
and the striae directed so are on the whole more weakly developed than the longitu¬ 
dinal ones. 
The skeleton of the shoulder girdle and the paired fins. 
Of the shoulder girdle we know with certainty only a part of the supracleithral, 
which is high as usual (Scl, Pl. 29, fig. 4). A fragment of the suprascapular is possibly 
present as well. Both these bones have been sculptured in the same way as the oper¬ 
cular bones. 
The pectoral fins (Pc, Pl. 29, fig. 4) are small and triangular. Their lepidotrichia 
are about 25 in number and are all ramified distally in the usual way. The two or 
three most anterior ones are unjointed for a short distance proximally; the others, on 
Text fig. 77. 
Acrorhabdus latistriatus n. sp. 
Parts of visceral skeleton after 
P. 170. Vt- 
Op, operculum; Po, preoperculum; 
Sop, suboperculum. 
