TRIASSIC FISHES FROM SPITZBERGEN 
229 
and typically Palaeoniscid-like (cf. Traquair, 1877 a, PL 1, fig. 5). With regard to the 
cleithral it is specially noteworthy that its anterior part, which is bent in a medial 
direction and helps to form the posterior boundary of the gill-chamber, is well preserved 
(text fig. 74 A, D, E, F). It is also noteworthy that the concavity in the lower part of 
its posterior margin is weak. The two cleithrals meet ventrally in the median line or 
at least come very close to each other. 
The two claviculae (Id, text fig. 74; PI. 3 i, figs. 2, 3 ; PL 32 , figs. 3 , 5) are relatively 
strong and large. Posteriorly they surround together the anterior ends of the cleithrals, 
ventrally they meet in a median longitudinal suture (text fig. 74 B), and dorsally too 
they have come into 
contact with each other, 
at least by means of the- 
process prc. Their dorso¬ 
lateral surfaces have 
helped to form the lower 
boundary of the gill- 
chamber. Seen in profile 
on the lateral side, each 
of the bones (text fig. 
74 C) is triangular, with 
one ventral, one caudal 
and one antero-dorsal 
margin, of which the ven¬ 
tral one is almost straight 
and the caudal one con¬ 
cave. The antero-dorsal 
margin is weakly con¬ 
cave or almost straight 
in its posterior half; 
anterior to this there 
comes a small but very 
marked sinus (sin. cor . 
post), which is bounded 
anteriorly by the pro¬ 
cess prc, and finally in front of this process another sinus which reaches to the anterior 
corner of the bone. This corner is truncate, while the other two more rounded. The 
postero-dorsal one is somewhat produced. Seen from the ventral side (text fig. 74 B) 
the two bones in question have somewhat convex lateral margins, and the suture 
between their medial margins appears to be rather straight. On each bone the anterior 
end is blunt and concave in such a way that with that of the other bone it forms a 
rather large sinus. 
A specimen of Acipenser ruthenus that I had an opportunity to investigate shows 
that in this species the clavicle is developed in nearly the same way as in Acrorhabdus 
bertili, not only in the general features but also in many details. Thus on the dorso- 
Text fig. 74. Acrorhabdus bertili n. sp. 
Parts of the shoulder girdle. After P. 174. 3 / 4 . 
A. cleithral, clavicle and primary girdle plate of the right side. 
B. Clavicles in ventral aspect. 
C. Left clavicle in lateral aspect. 
D. Primary girdle plate in its relation to the cleithral and clavicle. 
E. Section through shoulder girdle along line Z—Y. 
F. Section through shoulder girdle along line X— IF. 
Cl, cleithral; Icl, clavicle; See, ossified primary girdle plate; d. g, processes on the posterior 
margin of the ossified primary girdle plate; m. cor. arc. ant, anterior portion of muscnlus coraco- 
arcualis; m. cor. arc. post, posterior portion of musculus coraco-arcualis; 11, nerve canal; 
prc, process on the dorso-medial margin of the clavicle; sin. cor. post, sinus for the posterior 
portion of the coraco-arcualis muscle; v, process on the ventral part of the posterior margin 
of the primary girdle plate. 
