TRIASSIC FISHES FROM SPITZBERGEN 
l 9 3 
however, to establish with certainty whether this shape is the original one or 
whether certain lateral portions of the anterior part of the plate have been broken 
off. I call the plate in question preliminarily a pelvic plate. I shall return to its homo- 
logues below. 
As far as one can judge, the endoskeletal radials were 16 or 17 in number, of 
which the most anterior 4 or 5 seem to have articulated with the pelvic plate, while 
the remainder were situated caudally of this plate. 1 ) They were all divided into two 
segments, a proximal and a distal one, the latter being very short. 
The proximal segments have had a small cartilage epiphyse on each end. Otherwise 
each of these segments is occupied by a compact, somewhat hour-glass shaped ossifi¬ 
cation ( po , text figs. 68 A, B, PI. 23 , fig. 3 ), which, apart from a thin peripheral layer of 
lamellar character, consisted entirely of the same concellous substance as the replacing 
Text fig. 68. Birgeria mougeoti Agassiz. 
Skeleton on the ventral fins. Alter P. 104. */ 4 . 
A) Skeletal elements as preserved in the fossil. B) Reconstruction of the endoskeleton. The cartilaginous parts dotted. 
Mt, metapterygeal elements; Pv, pelvic plate; do, ossification in the distal segments of the endoskeletal radials po, ossification in 
the proximal segments of the endoskeletal radials. 
bones of the neurocranium, a fact that seems to show that we are here concerned mainly 
with endochondral bone. In Polyodon and possibly also in certain recent sturgeons, where 
a corresponding ossification is found in each proximal segment of the endoskeletal 
radials of the ventral fins, this ossification consists only of a rather thin perichondral 
bone layer (v. Rautenfeld, 1882, p. 26, PI. I, fig. 5; Regan, 1904, PI. VII, fig. v ). 
The distal segments, unlike the proximal ones, practically all consist of cartilage. 
It is intereting, however, that some few ot them, belonging to the middle radials, had 
a little ossification developed {do, text figs. 68 A, B; PI. 23 , fig. 3 ) 
*) Similar radials have been observed in Elpisopholis and Coccolepis . In Elpisopholis , according to Woodward 
( 1908 a, text fig. on p. 17), they are developed to about the same number as in B . mougeoti . In Coccolepis macropterus 
(Traquair, 1911 b, p. 14) there are only 9, in C . australis (Woodward 1895 a, b fig- 1 b)> on the other hand, about 25. 
Stensio, Triassic Fishes from Spitzbcrgen. 25 
