454 CLASSIFICATION OF DEVONIAN FISHES 
terior dorsal interspinous bones become so modified as to forma great 
shield-shaped dermal plate, with a strong inferior crest, which occupies 
the same position and has the same relations as the medio-dorsal plate 
of Coccosteus, though it commonly bears a strongly articulated spine, 
which is absent in the latter genus. In some species, as Arius cruciger, 
the principal plate is provided with lateral accessory plates, in which, 
perhaps, we have the homologues of the dermal plates 4, of Coccosteus. 
It is possible that ¢ may have been the operculum, which occupies a 
nearly similar position in 7s, but if it were suturally connected with 
Fig. 20A. Arius rita, after Cuvier and Valenciennes. 
the suprascapula, this view would be untenable, and the bone would 
have to be regarded as a scapular element. 
In the Siluroids to which I have referred, and in Lortcaria, a vast 
latero-ventral shield is produced by the prodigious expansion and 
coalescence of the bony elements which are homologous with those 
termed “coracoid” and “radius” in other fishes. Viewed from the 
ventral surface, these bones form four great plates, those of each side 
being closely united, or even amalgamated together, while the opposite 
pairs are joined, in the middle line, by a strongly serrated suture. 
When the pectoral fin is provided with an anterior spine, this is 
articulated by a curiously complicated joint with the so-called coracoid. 
The cornua of the hyoid are large stout bones, and the urohyal, alsoa 
large and strong bone, which is particularly broad in Lortcarza, con- 
nects the hyoidean with the pectoral apparatus. 
On comparing this apparatus with the sternal shield of Coccosteus, 
one is tempted to compare the antero-median piece of the latter with 
