554 vnov. t. w. bbidge on the mesial 



of the expansion of their distal extremities for the support of 

 the modified defensive and guard spines. It may further be 

 pointed out that, if the relations of the various radial elements to 

 the series of fin-rays be traced from behind forwards, no special 

 difliculty with regard to the mutual relations of the more anterior 

 of them need be experienced. It is only necessary to bear in 

 mind (i.) that in the normal portion of the fin each fin-ray is 

 supported by two contiguous radial elements, although it is to 

 the anterior of the two that the ray rightly belongs ; and (ii.) 

 that in the anterior portion of the fin the loss of the distal 

 segments of their proper radial elements has led to the backward 

 displacement of certain of the fin-rays (that is, the guard and 

 defensive spines), and also to their exclusive support by the 

 proximal segments of the radial elements immediately posterior 

 to those to which they really belong. In the light of these 

 considerations, it is an easy matter in the case of Platy stoma to 

 correlate the eight radial elements with the eight fin-rays in the 

 order of their sequence from before backwards. 



Anal fin. — In the anal fin there are thirteen radial elements 

 and sixteen fin-rays. The fourth to the thirteenth radial elements 

 (fig. 16) inclusive are composed of both proximal (/?.«.) and distal 

 {d.s.) segments, but without any trace of separable mesial seg- 

 ments. Each proximal segment is produced downward and back- 

 ward into a postero-inferior process { pi.p), precisely analogous 

 to the postero-superior processes of the dorsal fin, and, like 

 the latter, having the appearance and relations of a confluent 

 njesial segment. Each of the first three radial elements consists 

 of a proximal segment only, which has no trace of the postero- 

 inferior process of the succeeding segments. Concentration of 

 the fin-rays is apparent at each extremity of the series. The last 

 radial element supports two rays, while the first three support 

 between them the first five fin-rays, of which the third is the 

 normal ray of the first radial element. All the fin-rays have 

 cleft bases and, with the exception of the first five, their mode of 

 support is similar to that of the central and posterior rays of the 

 dorsal fin. In the absence of distal segments, the first five rays 

 are supported by the three anterior proximal segments. 



Amiurus catus. 

 Dorsal fin . — This fin is very similar to the corresponding fin 

 in the preceding species, and for an account of its structure and 



