524 Notices of Memoirs— Br. R. E. Traquair's Address, 



Again, in these Lepidosteid forms we have a repetition of the same 

 tendency for the thick rhombic, peg-and-socket articulating scales to 

 become rounded and imbricating, as we saw in the Crossopterygii 

 and again in the Paleeoniscidfe. To such an extent does this go that 

 in the recent Aviia, whose skeletal structure so clearly shows it to 

 belong to this group, the rounded scales are so thin and flexible that 

 after it was removed from the Clupeoid family, or Herrings, and 

 placed among the ' Ganoids," it was considered to be the type of 

 a distinct sub-order of ' Amioidei.' 



As the Acipenseroids dwindled away after the close of the great 

 Palajozoic era, and are now scantily represented only by the 

 degenerate paddle-fishes and sturgeons, so the Lepidosteid series, 

 flourishing greatly in the Trias and Jura, in their turn declined in 

 the Cretaceous, and in the Tertiary period became about as much 

 a thing of the past as they are now, the North American Lepidosteus 

 and Amia, of which remains of extinct species have also been found 

 in Eocene and Miocene rocks, only remaining. These two genera, 

 can, however, hardly be called ' degenerate.' 



But that the fishes which succeeded the Lepidosteids in populating 

 the seas and rivers of the globe were evolved from them there can 

 be no reasonable doubt, while it is equally clear that they branched 

 ofi" at an early period, as already in the Trias we find the first 

 representatives of the order of Isospondj'li, which contains our 

 familiar Herrings, Salmonids, Elopids, Scopelids, etc. For Dr. Smith 

 Woodward has not only definitely placed the Jurassic Leptolepidge 

 and OligopleuridEe in the Isospondyli, but also the Pholidophoridae, 

 which appear in the Trias and extend to the Purbeck. And it is of 

 special interest that in the Pholidophori the scales are still brilliantly 

 ganoid, and mostly retain the peg-and-socket articulation, while in the 

 allied Leptolepidee, although they have become thin and circular, 

 a layer of ganoine mostly remains. 



With the Isospondyli we now get fairly among the bony fishes 

 of modern type — Teleostei as we used to call them — to which other 

 sub-orders are added in Cretaceous and Tertiary times, and which 

 in the present day have assumed an overwhelming numerical pre- 

 ponderance over all other fishes. The prevalent form of scale 

 among these is thin, rounded, deeply imbricating, and with the 

 posterior margin either plain (cycloid) or serrated (ctenoid). But 

 that these ' cycloid ' and ' ctenoid ' scales are modifications from the 

 rhombic osseous 'ganoid' type we cannot doubt after what we have 

 seen. It is indeed strange that the same tendency to the change 

 of rhombic into circular overlapping scales should have occurred 

 independently in more than one group. 



Incompletely as I have treated the subject, it cannot but be 

 acknowledged that the palseontology of fishes is not less emphatic 

 in the support of Descent than that of any other division of the 

 animal kingdom. The modern type of bony fish, though not so 

 'high' in many anatomical points as that of the Selachii, Cros- 

 sopterygii, Dipnoi, Acipenseroidei, and Lepidosteoidei of the 

 Palaeozoic and Mesozoic eras, is more specialized in the direction 

 of the fish pi'oper. 



