23o 
ERIK A : SON STENSIO 
medial margin of each clavicle of Acipenser ruthenus one can distinguish a process {prc, 
text fig. 75), which has a marked sinus both in front and behind. As in Acrorhabdus 
bertili the process also comes into contact with the one on the opposite side. To judge 
from the figures given by Gegenbaur (1865, PI. 6, fig. 2) and Parker (1868, PI. 1, figs. 6, 7) 
the same process would also be present in Acipenser sturio, although there it is wider 
and not so strongly developed. 
In my specimen of Acipenser ruthenus, as text fig. 75 shows, one portion of Vetter’s 
(1878, pp. 480—482) musculus coraco-arcualis has its exit on the anterior side (m. cor. arc. 
ant) and one on the posterior side (m. cor. arc. post) of the process prc on the dorso-medial 
margin. The anterior portion, which is the stronger, passes off forwards and is related to 
the sinus situated in front of the process prc, while the posterior portion, which has 
principally a dorsal course, passes upwards through the 
sinus behind the same process. 
From what has been mentioned it seems very probable 
that the musculus coraco-arcualis in Acrorhabdus bertili was 
subdivided into two portions in the same way as in Acipenser 
ruthenus. It is also very noteworthy in this connection 
'“that in Acrorhabdus bertili (P. 174) we find a large, well 
9 developed urohyal {Uhy, PI. 3 i, fig. 2; PI. 32 , fig. 3 ) situated 
in the same way as in the Teleosts. I have already shown 
in this work (pp. 75, 87) that there is a urohyal in the Coela- 
canthids as well, and this bone can thus no longer be looked 
upon as being characteristic for the Teleosts alone, as 
Goodrich especially (1909, p. 350) maintained. 1 ) 
The sculpture on the supra-cleithral and the cleithral 
has the same character as that of the opercular, i. e. it consists of striation with the 
same direction as the axis of the animal (PI. 32 , fig. 4). 
The primary shoulder girdle in Acrorhabdus bertili is represented by a somewhat 
high, quadrangular bone-plate {See, text fig. 74, PI. 3 i, figs. 1— 3 ; PL 32 , figs. 3 , 5) which 
is rather thin on the whole. Of its margins one is directed forward, one downward, one 
backwards and one upwards and backwards. The one directed forward is concave and 
joins the transversal lamella of the cleithrum, which helps to form the posterior boun¬ 
dary of the gill-chamber of its side. The one directed backward, which is also concave 
and has somewhat above the middle a small, rounded, blunt process {g, text fig. 74 A, D), 
is visible behind the posterior margin of the cleithral. The one directed downwards is 
almost straight or weakly concave and has its anterior part against the ventral end of 
the cleithral, which there is arched towards the median line and has a nearly horizontal 
position. The one directed upwards and backwards is the shortest of the four margins 
and weakly concave. The anterior lower corner is pointed and produced forwards; the 
anterior upper one is rounded, the posterior upper one prolonged in a rather consider¬ 
able process (d) in a backward and downward direction, and the posterior lower one 
(V) is blunt and rounded. 
*) In Polypterus, however, formations have long been known (Muller, 1844, pp. 149—150; PI. 1, fig. 3) 
that may be looked upon as partly corresponding to the urohyal. 
Text fig. 75. Acipenser ruthenus. 
Left half of- shoulder girdle from the 
lateral side. 1 / l . 
Scl, supracleithral Lettering otherwise as 
in text fig. 74. 
