TRIASSIC FISHES FROM SPITZBERGEN 
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otherwise its posterior margin has to a considerable extent formed the anterior boundary 
for the orbital opening. Medially, where the bone reaches up on the dorsal surface of 
the ethmoidal region, it joins the postrostral and is attached anteriorly to the lateral 
rostral plate, which seems as a rule to be larger than other rostral plates. 
The membrane bones of the cheek. — With regard to the membrane bones 
of the cheek in the Coelacanthids it is possible to observe, as in the case of the 
cranial roof, certain fusions of elements that were independent in the Rhipidistia. The 
homologues of the lacrymal and the jugal of the Rhipidistids both probably form together 
the lacrymo-jugal of the Coelacanthids and the homologue of the preopercular of the former 
is probably so divided in the latter that the dorsal part of it has been fused with 
the squamosal and the ventral part with the quadratojugal. The two last-mentioned 
complex bones have for these reasons been called by me the squamoso-preopercular 
and the preoperculo-quadrato-jugal respectively. 
The lacrymo-jugal is an arched bone, whose anterior part reaches forward on the 
lateral surface of the ethmoidal region, while its posterior portion partly forms the 
posterior boundary of the entrance to the orbit. It is generally attached posteriorly 
both to the squamoso-preopercular and to the dorsal one, called by me the postorbital, 
of the three postorbitally situated cheek plates. In Wimania and possibly in Sassenia 
too, its conditions are somewhat different, as in these species it is joined only to the 
squamoso-preopercular, while its connection with the postorbital is made by means of 
a small independent plate. 
The postorbital, squamoso-preopercular and preoperculo-quadrato-jugal are situated 
in a vertical row behind the orbit. 
The anterior margin of the postorbital forms the upper part of the posterior 
boundary of the orbital entrance. In Coelacanthus, Wimania and Sassenia it does not 
reach backwards to the opercular, but the space between it and the last-mentioned 
bone is filled either by a dorsal part of the squamoso-preopercular (Coelacanthus, 
Welburn 1902) or by an independent bone-plate (Sassenia), which in its turn may also 
sometimes be strongly reduced or be absent (Wimania). On the other hand in Macropoma 
(Woodward 1909) and if Reis (1888; 1892) and Woodward’s (1898a) view is correct, in 
Jurassic forms as well, the postorbital comes into direct contact with the opercular, 
and thus in all these latter forms it seems not quite equivalent to the bone that is denoted 
by the same name in the older ones. 
The squamoso-preopercular is the largest of the three postorbitally situated cheek 
plates and in the oldest forms (Coelacanthus) it has a more primitive character than in 
the younger ones on account of its extension behind the postorbital. Wimania and Sassenia 
occupy in this respect a typical intermediate position. 
The preoperculo-quadratojugal is so situated that it corresponds to the lower part 
of the palatoquadrate and the articulation between this and the mandibula. 
While in Coelacanthus and, as far as we know up to now, in the Jurassic and 
Cretaceous forms too, the cheek plates have, at least to some extent, had their margins 
closely joined together and have fitted rather well together with one another, in 
others, as e. g. Wimania and Sassenia, they have been separated from each other by 
more or less large interspaces, which means that they were more or less in a process 
