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ERIK A : SON STENSIO 
it looks as if it comprises both the homologue of the dermosphenotic of the Rhipidistids 
(the postfrontale in the sense of a membrane bone) and the homologues of one or more 
of the posterior supraorbitals Of these fishes. 
Neither in Coelacanthids nor in Rhipidistids have we previously had sufficient 
knowledge of the membrane bones on the ethmoidal region to enable us even approximately 
to compare them with those of the Stegocephalians. It is true that Watson and Day’s 
observations on the Osteolepis and Glyptopomus published in 1916 and Birks’ paper on 
Megalichthys published the same year constitute a great advance in this respect, but it 
is only on the basis of the results given above, arrived at by my investigations of 
Eusthenopteron, Dictyonosteus and the Coelacanthids, that we are able to attain to some 
extent a real understanding of the arrangement and morphological value of the bone 
elements in question. — It is especially noteworthy in this connection, as we have 
seen, that the Coelacanthids too have preserved a rather primitive character, in this respect. 
As far as we know (cf. text figs. 43, 44, 51, 57, 58) the membrane bones on the dorsal 
surface of the ethmoidal region both in Rhipidistids and Coelacanthids are arranged in 
the following way. 1) Farthest laterally we find on each side a number of rather small 
nasal elements or one larger nasal plate, apparently formed by fusion of a number of 
originally inedpendent elements. In Dictyonosteus there are three nasal elements on each 
side; in Eusthenopteron, on the other hand, they seem to be fused into one plate and in 
the Coelacanthids not only in this the case but the nasal elements may also have fused 
with the antorbital elements as well. As the original number of nasal plates on each 
side seems to have been at least three, I shall speak of a nasal series of elements in 
the continuation. This series is pierced by the supraorbital canal and is also characterized 
by its position on the dorsal side of the nasal capsule and by the fact that it always 
forms the dorso-medial boundary of the external nasal aperture(s). 2) Medially of the 
nasal series there is usually one paired, fairly large bone-plate, the postrostral, which meets 
that of the opposite side in a median suture. In Dictyonosteus and certain Coelacanthids the 
postrostral is represented on each side by an anterior and a posterior plate, in Eusthenopteron 
and a number of Coelacanthids, on the contrary, only one larger plate is present. It is 
probable, however, that the original number on each side was at least two, a view that 
seems to be also supported by Watson and Day’s restorations of Osteolepis, provided 
that these are correct. 3 ) A paired or unpaired bone-plate, generally rather small, is 
always wedged in between the anterior ends of the postrostrals (or their most 
anterior elements). I have chosen the name of interrostral for this.. 4) A series 
usually consisting of a number of rather small elements which I have termed 
rostrals, extends across the anterior end of the snout immediately in front of the 
nasal series, the postrostrals and the interrostral (possibly interrostrals, if it was 
paired). Anteriorly the rostrals are bounded by the premaxillae and an additional 
characteristic of them is that they are pierced by the ethmoidal commissure between 
the infraorbital sensory canals. 
It is of special importance to note in this connection too that the premaxillae in 
both Dictyonosteus and Eustenopteron do not extend on to the dorsal surface of the 
ethmoidal region or do so to only a very slight extent; they are very low and give 
the impression of having arisen by fusion of bases of teeth (cf. Allis 1919 a). 
