TRIASSIC FISHES FROM SPITZBERGEN 
23i 
In a dorsal direction the primary shoulder girdle plate has not by far the same 
height as the cleithral (text fig. 74 D). Ventrally the two primary shoulder girdle plates 
come near each other, and this is especially the case with, their anterior lower corners, 
which were probably connected by ligaments. 
Only the dorsal half of the primary shoulder girdle plate is in contact with the 
sagittally placed lamella of the cleithral. For between the ventral half of the shoulder 
girdle plate and the ventral part of the cleithral a fossa is developed which opens 
backwards and downwards. This fossa, into which the ventral musculature of the pectoral 
fin extended and had its origin, is rather deep in the direction from front to back, but 
narrow in the transversal direction. In its roof a wide, short nerve canal (n) has its 
opening. This canal pierces the primary girdle plate in an upward and medial direction, 
then continuing on its medial side as a wide, ascending furrow. A section through the 
primary shoulder girdle plate near the lower end of the nerve canal (along the line 
X—U in text fig. 74 D) is shown in text 74 F. Another similar section, taken farther 
dorsally (along the line Z—Y in text fig. 74 D) is figured in text 74 E. In the latter 
section one finds that the canal is continued by a deep sulcus, which is bounded 
anteriorly by the transversal lamella of the cleithral, posteriorly by a vertical torus on 
the medial side of the primary girdle plate (this torus is shown in the cross section as 
a medially directed process). 
The pectoral fin must have articulated with the primary shoulder girdle plate in 
neigbourhood of the little process g. No canal for the dorsal fin musculature is developed. 
Finally with regard to the primary shoulder girdle plate it is noteworthy that it 
consists throughout of the same sort of cancellous bone substance as the replacing 
bones of the neurocranium. 
The account and figures given here ought easily to make it clear that the primary 
shoulder girdle in Acrorhabdus bertili is not closely related either to that of the sturgeons 
or of Amia and the Teleosts. While a wide canal for the dorsal musculature is already 
found in the sturgeons and the development of this has proceeded farther in Amia and 
the Teleosts (Gegenbaur 1865, pp. 95-—135) a canal of this short is lacking, as we have 
seen, in Acrorhabdus bertili, which in this respect seems to have remained at a primitive 
Selachian-like stage of development. 
The pectoral fins (Pc, Pl. 32 , fig. 4) are incompletely preserved and consequently 
no details can be given either as to their shape or size. All their lepidotrichia, except 
the two or three most anterior ones, are densely jointed right to the base and are 
furnished with a fine ganoine striation in a longitudinal direction. 
The judge from P. 172 the small ventral fins are situated about half-way between 
the pectoral fins and the anal fin. They are poorly preserved, and it is only possible 
to establish that their lepidotrichia were jointed throughout their length. 
Squamation. 
The squales in Acrorhabdus bertili are mostly wider than high, and this is specially 
strongly marked on the ventral side and towards the dorsum, where their height is 
sometimes only 1 / s — T / 6 of their width. Only immediately behind the posterior part of 
the supracleithral and the upper part of the cleithral do we find in a couple of vertical 
