306 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
X.—PELVIC ARCH AND FIN. 
The pelvic arch consists of two similar pieces united in the middle 
line. The anterior part of each piece is very thin, and is produced 
into a point at the outer angle. The posterior edge is rounded, and 
gives articulating surfaces for the rays of the ventral fin—eight in 
number. Posteriorly in the middle line there is a horse-shoe shaped 
cartilage, the concavity of which is directed backwards, the two 
limbs of which give attachment to portions of the infracarinales 
muscles. Criste for the attachment of muscles traverse the thin 
portion, and the posterior border is edged with cartilage. According 
to Davidoff’ these bones are not homologous with the pelvis of the 
Elasmobranchs, but correspond to the metapterygial basalia much 
enlarged. The pelvis of Am/wrus corresponds very closely to the 
description of that of Barbus fluviatilis given by the same author, 
the horse-shoe shaped cartilage representing the stout posterior pro- 
cess as in that form. 
The reduction of the radialia which characterises the Teleosts 
when compared with Elasmobranchs and Ganoids is here carried to 
its greatest extreme, these structures being entirely absent. The 
fin-rays have the usual character. 
Having now described the structure of the various parts com- 
posing the skeleton of this Siluroid, it remains to point out one or 
two generalizations with regard to it. In the first place its relation 
to the Cyprinoids is close, as evidenced by the modifications of the 
anterior and the tail vertebre, and also by the relations of the audi- 
tory apparatus. 
Secondly, there is evidence that the Siluroids have branched off 
at a very early period from the primordial Teleosts. This is shown, 
as has been already stated, by the almost complete ossification of the 
skull, and also by the extent of the specialization of the various 
parts. The canal for the orbital muscles has almost disappeared, 
showing that Amiwrus has passed through a stage in which it 
possessed a complete canal, a stage in which the Cyprinoids still 
remain. The perfectness of the arrangements for the fixation of the 
1 Davidoff —Beitrage zur vergl. Anat. d. hinteren Gliedmasse d. Fische. Morph. Jarhb. VI. 
1880. 
