TRIASSIC FISHES FROM SPITZBERGEN 
4 1 
a reduction of originally stronger ossifications. In the case of the Stegocephalian orders 
mentioned a reduction of this sort has been clearly shown by Watson (1919) and with 
regard to the Coelacanthids I have myself already pointed out in this work that the 
same thing can be observed, at least in the orbitotemporal region. 
In the Temnospondylous and the Stereospondylous Stegocephalians and especially 
in the more primitive forms among them, the occipital region is well ossified. As Watson . 
(1919, pp. 62—63) has pointed out, everything indicates that this was also the case in 
their ancestors too. On the other hand, in the Mesozoic Coelacanthids, as we have seen, 
the same region has, to a very great extent, been cartilaginous. A basioccipital is 
known with certainty only in one genus, Undina, and it is impossible to decide whether 
a slight degree of ossification like this is to be regarded as primary or secondary, as 
we do not know the conditions either in the more primitive Palaezoic representatives 
of the Coelacanthids or in the Rhipidistids. 
With regard to the occipital region it is thus impossible to decide with certainty 
whether it offers any common features of a more special nature in fossil Crossopterygians 
and primitive Tetrapods. 
If, on the other hand, we pass to the labyrinth region, we undoubtedly find better 
agreement. In the more primitive Temnospondyli and Stereospondyli both the prootic and 
the opisthotic are as a rule developed, but in more specialized, youger forms, on the 
contrary, these bones are reduced (Watson 1919, pp. 62—63; Broom igi3 e, pp. 573— 
574, 583 — 588). The opisthotic, when present is, however, often found fused with the 
lateral occipital or in exceptional cases (Pteroplax) with the prootic (Watson, 1912 a, 
p. 7; 1916, pp. 612 — 618, 63o—632; 1919, pp. 14, 26, 50—59, 62 — 63; Broom 1913 e, 
PP- 573, 574, 583, 584, figs 6 B). 1 ) The prootic of primitive forms (Huene, igi3, pp. 3i8 
—322, 378; Broom, 1913 e, pp. 574, 587; Watson, 1912 a, p. 7; 1916, pp. 615—616, 
fig. 1; 1919, pp. 19, 23, 26, 52, 55, figs. 11, 12, 14, 16; Wiman, 1914 b, pp. i3, 19; 
PI. II, fig. 5,6; PI. V, fig. 4) 2 ) extends in a dorsal direction up towards the cranial roof 
in such a way that its uppermost part bears a considerable resemblance both in shape 
and position to the dorsal process (fj), from the prootico-opisthotic of the Coelacanthids. 
The lower part of the same bone, on the other hand, may even in the primitive forms not 
infrequently be thin and weakly developed but it seems from Watson’s exposition 1919 (pp. 
5 1 — 59) that it originally in the earliest Stegocephalians ought to have been strong and to have 
at least to some extent resembled its homologue in Coelacanthids. Finally it is especially note¬ 
worthy that the autosphenotic («postorbital ossification*, «postfrontal» in the sense of 
substitution bone), which is otherwise so distinctive a feature for the majority of the 
Teleostomi, is lacking both in the Coelacanthids and Rhipidistids just as in the Tetrapods. 
J ) The opisthotic of Wiman’s descriptions (1914 b; 1916 b, 1917) may after all be only a ventral process from 
the tabular. At least in Platystega and Lyrocephalus I have found the opisthotic as an independent bone, lying 
immediately anterior to the exoccipital. In Lyrocephalus (PI. 20, fig. 4) however, it is very small. 
2 ) In PI. 20 fig. I have figured the prootic of Lyrocephalus euri. In the specimen figured it is undoubtedly 
an independent rather thin and short plate of bone pierced by a foramen probably for the facialis nerv. After all 
this plate has had no direct relation to the labyrinth and might correspond to a dorsal part of the same bone in Eryops 
The prootic and sphenotic of Wiman’s description 1916 (1916 b, pp. 21^—218; PI. XVI, fig. 4) are only parts of 
the otic process of the epipterygoid, as can clearly be seen from the figure published by me on PI. 20, fig. 3 (cf. 
Watson, 1919, pp. 28, 52, 58, figs. 12, 14). 
