BY WILLIAM A. UASWELL, M.A., B.Sc. 3 



cartilage just described is not represented in that order. The 

 remaining framework of the paddle shews an arrangement unique 

 among the Yertebrata. Erom the middle of the basal cartilage 

 a series of about twenty-six quadrangular pieces takes its orioin 

 forming a longitudinal axis along the middle of the paddle to its 

 extremity. The pieces gradually become smaller and are scarcely 

 distinguishable towards the end of the paddle. On the two 

 posterior corners of each ]3iece a branch is inserted runnin-^ 

 obliquely backwards towards the margin of the fin ; the branches 

 of the first eight or twelve pieces are three-jointed, the remainder 

 two- jointed, the last having no branch at all. Slight irregularities, 

 such as the origin of two branches from one side of a central 

 piece occur, as also several four-jointed branches immediately on 

 the basal cartilage." 



On this description Huxley* makes the following comments : — 



" In general, this description suits the pectoral fins of the 

 specimen I have described very well. Mine, however, has 

 only twenty median cartilages. All but the very last bear 

 lateral rays ; but towards the distal end of the fin these become 

 minute, and consist of a single piece. Moreover the distal 

 joints are much more slender, especially the last. A more 

 important point is that the second shews no trace of such 

 divisions as those described by Dr. Griinther. To make sure of 

 this I made a thin microscopic section of this cartilage on the 

 right side, and thereby satisfied myself of the homogeneity of 

 the cartilage of which it is composed." 



"I find no true joint between the proximal median piece and 

 the scapular arch, the connection between the two being effected 

 by a solid fibrous mass." 



Eig. 2 is copied from Huxley's figure of the pectoral fin of 

 Ceratodus. 



P.Z.S., 1876, p. 46. 



