TRIASSIC FISHES FROM SPITZBERGEN 
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would according to Sagemehl be caused by the «squamosal» developing more and more as 
a substitution bone in the capsula auditiva, so that the primary part of the opisthotic 
would be thrust aside and could not be developed. As has been pointed out above, 
he took the opisthotic in Amia to be a substitution bone. 
Several years before Sagemehl-Vrolik (1873) had already shown convincingly that 
the bone called the opisthotic in the Teleostei is only a membrane bone, and because 
of this he introduced the new name of intercalar of it. Later on Allis (1899) especially 
adopted this view, and he too, as has already been pointed out, definitely states that 
he found that the opisthotic of Amia belonged to the category of membrane bones. The 
embryological investigations so far carried out on some Teleostei seem to show that the 
so-called opisthotic (intercalar) in these is formed exclusively as a membrane bone 1 ) 
Schleip, 1904, pp. 379— 38 o; Gaupp, 1905, pp. 677—678, Boxer, igi 3 , p. 385). 
It is clear from what has been stated that we ought to adopt the name intercalar 
in the sense of a membrane bone for the so-called opisthotic of the Teleostei and Lepi- 
dotus. If Allis’s account is correct the same term ought also to be used for the so- 
called opisthotic in Amia. In Polypterus, according to Allis (1899), the intercalar seems 
to be fused to the cartilage bone that forms the caudal part of the labyrinth region. — 
Because of its nature as a fibrous ossification the intercalar cannot possibly be homo¬ 
logous with the opisthotic in the Tetrapods (cf. Allis, 1897 b, p. 21; 1899) which, as we 
know, is a cartilage bone that is developed in relation to the posterior part of the labyrinth. 
Among the recent Teleostomes it is easiest in Polypterus 2 ) to find a homologue to 
the opisthotic of the Tetrapods, as we have seen from the above summary of the 
literature. In this fish the opisthotic seems, together with the epiotic and intercalar, to 
form part of the large ossification that occupies the labyrinth region and is pierced by 
n. glossopharyngeus. 3 ) 
In the Teleostei the conditions of the pterotic and lateral occipital are such that a 
component of the opisthotic seems to form part of each of these bones. The opisthotic 
component in the pterotic would then be represented by the part that consists of car¬ 
tilage bone. In the lateral occipital the opisthotic component would have its correspon¬ 
dence in the part that extends forwords in the lateral wall of the labyrinth region. The 
opisthotic might thus be divided over two of the adjacent bones. 
It seems rather probable that the dorsal part of the opisthotic is reduced in Lepi- 
dosteus. The ventral part, on the other hand, might perhaps be divided over the lateral 
occipital and the prootic. 
In Amia the reduction of the opisthotic has proceeded much farther, and it is very 
uncertain whether anything is left of it. If this were the case the remaining part would 
perhaps have fused to the prootic. 
Among the fossil Teleostomes we find in the Coelacanthids nothing developed of 
the dorsal part of the opisthotic. On the other hand the ventral part seems to have been 
present in these fishes, as has been shown above (p. 54—61) although fused to the prootic. 
r ) The bone described by Woodward (1915, P- 38) in Lepidotus under the name of opisthotic seems in all 
respects to show almost the same conditions as the intercalar (so-called opisthotic) in the majority of the Teleostei. 
2 ) I except here the conditions in Calamoichthys, which are still very incompletely known. 
3 ) This is evident in the large specimen investigated by me. 
