No: 3.) CHEEK AND SNOUT OF AMIA CALVA. 443 
costeus and Chlamydoselachus, the canal in the former animal 
traversing the so-called supratemporal bone, which Pollard con- 
siders the homologue of the preoperculum. In Polypterus, also, 
a bony connection is found at this same place, wholly unasso- 
ciated with a lateral canal, according to Traquair’s descrip- 
tions, but, according to Pollard (No. 31, p. 548), associated 
with rudiments of such a canal. The prosquamosal of Tre- 
matosaurus and the supratemporal of Coccosteus are certainly 
the homologues of the supratemporal of Capitosaurus, which 
bone also forms a bony connection between the two lines of 
bones here under consideration. This bone of Capitosaurus, 
which is not said to be traversed by a lateral canal, is con- 
sidered by, Gaupp (No. 17, pl 10s, PI Vil, Pig. 11) as the 
homologue of the paraquadratum of his descriptions of other 
vertebrates. 
In Trematosaurus, the preopercular canal, after leaving the 
prosquamosal, enters, as already stated, the jugal, which bone 
extends forward under and beyond the eye, but lies wholly 
posterior to the maxillary bone. The jugal of Trematosaurus 
is thus the apparent homologue of that part of the compound, 
so-called maxillary bone of Polypterus that lies either posterior 
to, or postero-superior to, the maxillary element of that bone, 
fused, perhaps, with one or with both of the bones designated by 
Traquair as bones y/ and y'’. What the homologue, in Polypterus 
or in Amia, of the quadrato-jugal of Trematosaurus may be is 
not evident. In Polypterus it may be represented by bone y”. 
It is not traversed in Trematosaurus by the preopercular canal 
of that animal, and hence cannot be one of the bones developed 
in connection with that line of organs. As it becomes interca- 
lated, in certain reptiles, between the prosquamosal and jugal 
(No. 6, Fig. 1), it may possibly represent that part of the 
preoperculum of Amia that lies distal to the horizontal cheek 
lines of pit organs, or be a bone that is developed in connection 
with the vertical and mandibular cheek lines of organs, and 
either not found as a separate bone in the skull of Amia or 
found as the supra-angular. It is to be noted that the quadrato- 
jugal in the Stegocephali may take part in the formation of the 
mandibular articulation, either as “ Ansatz an das Quadratbein 
