ERIK A : SON STENSIO 
the orbital opening; its antero-ventral and dorso-medial margins bound the bones that I 
shall describe immediately below. The centre of ossification lies dorso-medially of the 
anterior nasal aperture. 
The ethmoidal region is covered between the nasalo-antorbital of both sides by a 
rather large paired plate which, as I have already mentioned in. describing IF. sinuosa, 
I propose to call the postrostral ( Ptr, text figs. 3 g, 40, 43, 44; PI. 11-—1 3 ; PI. 14, figs. 1 — 4). 
The two postrostrals are oval in shape and their maximum breadth is about half their 
length. With their longitudinal axis they converge a little in anterior direction and 
with their medial margins they meet in a rather short median suture that forms the 
direct anterior continuation of the median suture between the fronto-dermosphenotics. 
The)’ rest with their posterior portions on the anterior ends of the last-mentioned bones 
and with their lateral margin each of them meets the nasalo-antorbital of its side and 
the anterior supra-orbital. plate. The centre of ossification is situated a little in front of 
the middle. Otherwise there is nothing else to remark about these bones, except that 
they lie in a plane that forms the direct continuation of the fronto-dermosphenotics and 
consequently face dorsally and somewhat anteriorly. 
In the angle between the anterior ends of the postrostrals there has been, as far 
as one can judge, a little double or single bone plate (Ir, text figs. 40, 43; PI. 14, figs. 1—4;) 
which I have called the inter-rostral. 
In front of the nasalo-antorbitals, postrostrals and interrostrals is found a transverse 
row of four-sided bone-plates (R, text figs. 39, 40, 43, 44, Pis. 12, i 3 ; PI. 14, figs. 1—4) 
which might properly be called rostrals. The middle ones in their posterior part reach 
up to the dorsal surface of the ethmoidal region, while their anterior part covers the 
forward pointing surface of the same region and thus faces straight forward or even a 
little ventrally. The lateral rostral plates on the other hand belong more to the sides 
of the ethmoidal region. The total number of the rostrals cannot yet be fixed but there 
were probably not less than four or more than six of them. The centre of ossification 
is plainly marked in most of them. 
It is evident merely from their topographical position that the bone-plates which 
I have mentioned respectively as the rostrals, the interrostrals and the postrostrals 
correspond to a large extent to a number of bone-plates found in the same position in 
the Rliipidistia (Watson and Day 1916) and the so-called «supraethmoid» of the Teleosts. 
I shall not, however, in this connection deal with the question of their homologues. 
All the bones in the cranial roof of A. robusta have a very characteristic sculpture 
(PI. 16, fig. 4), consisting of fine, close, transversal striae and tubercles. A similar transversal 
also distinguishes the four middle extra-scapulars, while each lateral one is striated 
longitudinally in the same way as the scales. 
As far as one can judge from the sclerotic ring ( Scr, text fig. 44; Pis. 11 — 13 ; 
PI. 15, figs. 1, 5), the eye was larger than in IF. sinuosa. The sclerotic ring was probably 
formed by about twenty plates of the usual four-sided shape. 
The membrane bones of the cheek. 
The membrane bones of the cheek must have been much reduced and are subdivided 
in a great number of small scale-like plates (PI. 15, figs. 1, 2). The sculpture on these 
