1889. ] EOCENE SILUROID FISHES. 203 
other, so that the centra appear as one bone closely united to the 
basioccipital, and at their point of union with the latter bone there 
is a strong downwardly directed process. 
The Arius skull most closely resembling this fossil is one in the 
British Museum, which Dr. Giinther assures me is almost certainly 
Arius gagorides. The correspondence between this and the fossil is 
so close as to leave no doubt as to their generic identity, and the 
following comparisons refer to this specimen. I have to acknowledge 
my indebtedness to Dr. Giinther, who on this, as on many other 
occasions, has spared no trouble in order to facilitate my examination 
of the specimens under his charge, thereby enabling me to settle the 
affinities of this fossil fish in a manner which would not otherwise 
have been possible. 
The frontals of A. gagorides (fig. 8, fr.) differ from those of the 
Barton fossil in having the median cleft extended further backwards, 
and their hinder ends are proportionately wider. The latter cha- 
racter is in relation to the form of the sphenotics, which are relatively 
narrower at their hinder part than is the case in the fossil. 
In ordinary bony fishes the post-temporal is connected with the 
skull by two processes, one of which is attached to the pterotic 
(squamosal) and the other to the epiotic; but the post-temporal of 
A. gagorides has in addition to these a third attachment by means 
of a long bar extending from its under surface to the base of the 
skull (fig. 9), and in addition to this there is a thin plate of bone, 
which may be a process of the post-temporal, extending under the 
epiotic to the transverse process of the vertebrae. The two upper 
processes of the post-temporal are ornamented on their upper 
surface with tubercles, and between them aud the pterotic an opening 
is left which seems to vary in extent in different specimens. The 
bone to which the hinder of these processes is attached appears 
from its connections and relations to the auditory region to be the 
epiotic; but it may be the parietal. If the latter be the correct 
interpretation, then the ossicle behind it may be the epiotic; and 
the hinder process of the post-temporal certainly reaches thus far. 
On the other hand, if the parietal be absent and this bone be the 
epiotic, then the hinder plate will probably be a supernumerary 
temporal plate, wedged in between the wide hinder moiety of the 
supraoccipital and the epiotic. 
The post-temporal bone cf Arius gagorides has the same structure 
and relations as that described in the Barton skull; but the opening 
left between its two upper processes is not seen in the fussil. This 
feature, however, varies even in the recent species, and in the fossil 
the two processes evidently have joined and obliterated the space. 
The pterotic and parietal elements are larger than in the fossil, the 
last-named bone reaching to the margin of the bony cephalic shield, 
while in the fossil it seems probable that the epiotic and post-tem- 
poral bones excluded it from the margin. 
The supraoccipital of A. gagorides is an elongated bone con- 
stricted in the middle, the portion in front of the constriction 
corresponding with the part preserved in the fossil. In the main 
