BY WILLIAM A. IIASWELL, M.A., B.Sc. 7 



])aired and unpaired fins might have been inferred from their 

 adult structure as ^vell as from their mode of development. 



Both Giinther and Huxley, as already noted, found both the 

 pectoral and pelvic fins to be uniaxial. I was surprised, there- 

 fore, to find that the skeleton of the pectoral fin of the first of 

 two specimens very kindly placed at my disposal by Mr. Kamsay, 

 presented the arrangement shewn in fig. 1. 



There is first an elongate basal joint attached to the shoulder- 

 girdle ; upon this follows a short transversely oblong joint and 

 to the distal border of this in turn are connected (1) a series of 

 five post-axial rays, (2) the main axis of the paddle consisting 

 of a series of cartilaginous joints to most of which are attached 

 a pair of jointed cartilaginous I'ays, and (3) a supplementary 

 axis (pre-axial fin-ray of Huxley) consisting only of four joints, 

 and having only two rudimentary rays, one attached to the 

 anterior and distal angle of the first joint, and the other to the 

 same point on the second. The fin of the opposite side presented 

 the same arrangement of the cartilaginous elements, except that 

 the anterior axis had only one rudimentary ray in place of t'wo. 

 On examining the pectoral fins of a second specimen of Ceratodiis 

 I found that the anterior axis of neither of them had any 

 rudiments of rays. 



When the left pelvic fin of the first specimen was examined, a 

 still greater divergence from the archipterygial type of structure 

 presented itself. Articulating with the basal joint are (1) in 

 front two small cartilages of irregular shape, the anterior of 

 which supports a short ray, and (2) a broad, somewhat oblong 

 plate. This plate is seen on a closer inspection to present traces 

 of longitudinal division into two parts and is formed apparently 

 by the partial coalescence of the bases (1) of a short bifurcated 

 ray, (2) of a short branching anterior axis suj^porting five rays, 

 (3) of the basal undivided portion of the main axis, and (4) of a 

 short posterior axis giving off one simple and two bifurcated 

 branches. Of the rays attached to the distal portion of the axis 



