THE DERMAL FIN-KAYS OF FISHES. 505 



whole quite similar to those of Ceratodus. They have a 

 distal region^ which is regularly jointed^ and a proximal 

 regioD without articulations (fig. 35). It is this region which 

 Pander evidently mistook for the endo-skeletal fin-supports. 

 The proximal unsegmented piece is covered over by the 

 thick body-scales, lu particularly well preserved fossils 

 the segments cau ofteu by seen to be of very unequal length 

 (this is, at all events, the case in Dipterus macropterus) ; 

 they may be much shorter proximally than in the more distal 

 region, as is the case in so many Teleostomes. Never is 

 there to be seen on the rays the grooved and pitted surface 

 and the ganoine layer characteristic of the superficial scales. 

 The dermal rays are of essentially the same structure in all 

 the fins, whether paired or unpaired (figs. 27 and 58). 



On examiniug, in these specimens, the anterior edge of the 

 second dorsal, tlie anal, and of the paired fins, and the lower 

 edge of the caudal fin, we find series of small bright scales 

 lying along the extreme edge of the fin and extending some 

 way up the dermal rays (figs. 27 and 58). They have been 

 indicated in the figures of Dipterus given by Huxley (18) 

 and A. S. Woodward (42). These scales, of oval or oblong 

 shape, are of considerable thickness, are covered with an 

 external layer of ganoine, and ornamented with grooves and 

 pits, just as is the case with the ordinary body-scales (fig. 28). 

 They also resemble the body-scales and head-plates in histo- 

 logical structure (figs. 38 and 39). In fact, there can be no 

 doubt that the fin-scales are homologous with the body-scales, 

 and there can also be no doubt that they are not merely 

 fulcral scales, comparable to those of the Actinopterygii. 

 The small fin-scales just described undoubtedly lie at a higher 

 level than the camptotrichia, which are below them. They 

 appear to correspond in position and length with the 

 segments of the rays, but are not articulated so close 

 together end to end as are the consecutive segments of the 

 underlying dermal rays. It is to be noticed also that they 

 are much broader, and that whilst in the camptotrichia of 

 Dipterus, and indeed to some extent of all Dipnoi, the articu- 



