431 



the specimen was in when handed to me, be decided. The animal was 

 a male of about the same size as the first example. 



Reverting to specimen No. 1 the complex nature of the accessory 

 portions is of some interest and suggestive of homologies. Firstly, it 

 may be noted that the parts, although practically median as regard 

 attachment to the body, in structure are to be regarded rather as 

 paired than as median fins. This of course supports the view of 

 their fundamentally similar nature. How are we to look upon the 

 whole appendage? It may be regarded as a single fin. In such a 

 case the part a. Fig. 2, consisting of five well developed pieces would 

 repi'esent basalia while the remainder {h and c) would constitute the 

 radial portion of the fin. The structure of b consisting as it does of 

 radials only, supports such a view, but against it are the facts that c 

 in itself already possesses basalia — is indeed a complete fin — and that 

 the radials arise from only one of the assumed basal elements, the 

 remaining four carrying none. On the other hand a may be regarded 

 as a girdle, while b and c are fins. If this view is taken then the 

 fins represent two distinct stages of development. Fin c has no 

 basals and is comparable to the primitive Cladoselache condition 

 or to a simple median fin. Fin & is a uniserial ichthyopterygium. 

 From any point of view the whole structure is perplexing ; yet without 

 doubt the noteworthy fact is brought out that in this abnormality, 

 which is possibly the outcrop of a migrant germ cell, a combination 

 occurs of varied conditions, which are represented in different Elasmo- 

 branchs. Thus is emphasised a phylogenetic relationship. 



The material provided by specimen No. 2 does not furnish data 

 for further consideration than has already been given. 



Bateson (Materials for the study of variation, p. 540) quotes 

 several cases of extra fins in Raiidae, which seem to be of a similar 

 nature to that in speciemen No. 2. 



My thanks are due to Mr. G. Sim, A. L. S., through whose 

 courtesy I was permitted to examine the fishes under consideration. 



