FINS OF ELASMOBRANCHS. 457 
the dorsal postaxial angle of which a tall iliac process (il) extends dorsad. Behind 
the root of this process is another (a), which is the articular surface for the basal cartilage 
of the ventral fin. From the outer dorsal and outer ventral parts of the ischio-pubic 
cartilage two cartilaginous bars proceed preaxiad for some distance, and then meet, thus 
enclosing a space (0), which may be called an “ obturator foramen.” 
THE Prctorau Fin (Plate LX XIX. fig. 3). 
The skeleton of this fin presents only two basal cartilages, whereof the preaxiad one 
(p), short and quadrate, must, I think, be deemed the propterygium', while the other 
much elongated one (m) must include the mesopterygium as well as the metapterygium, 
unless we consider the former to be absent. Annexed distally to the propterygium is 
a triangular cartilage?, which appears to consist of, or to represent, parts of the four 
most preaxiad radials in one mass. 
At the distal end of the metapterygium is an hexagonal cartilage, whence no less 
than fourteen radials diverge, coalescing in various ways so as to produce a curious kind 
of mosaic pattern. Eleven radials are attached to the distal margin of the meta- 
pterygium; and two pairs of these coalesce together proximally for a short space. 
Almost all the radials have a small cartilaginous segment appended to their distal end ; 
and these small cartilages increase very gradually in size, from the one attached to 
the triangular preaxiad cartilage, to that of the last metapterygial radial: thence they 
decrease in size postaxiad with much greater rapidity. Minute extra cartilages are 
intercalated between the apices of the last radial attached to the metapterygium and 
those of the three or four next postaxiad—one between each. 
The proportion borne by the cartilaginous skeleton to the whole fin is small ; and it 
projects distally more towards the postaxial than towards the preaxial limb-margin. 
Compared with the pectoral of Chimera ®, the coalescence at the bases of the radials 
is less, save near the distal end of the metapterygium, where it is more. ‘The series of 
small distal cartilages is less complete ; but this may be due to the defective condition of 
the specimen at my disposal. 
POLYODON FOLIUM. 
Venrrat Fry (Plate LXXVIIL fig. 8). 
The ventral fin of this fish exhibits a most interesting structure, although unfor- 
tunately I have been able to examine only a dried specimen. The interest consists in 
the fact that the cartilaginous skeleton is made up exclusively of elongated radials 
' Tt is also thus designated by Gegenbaur in Chimera. 
2 This is referred to the mesopterygium by Gegenbaur in Chimera; but with such an interpretation I 
cannot agree. It seems to me to have no warrant, and to tend to mislead. 
3 As represented by Gegenbaur, ‘ Untersuchungen,’ pl. ix. fig. 15, 
38Q 2 
