PEDIGREES. 179 



scales, very thick and closely set, forming a 

 kind of pavement or mosaic ; that is to say, they 

 did not overlap. 



The accompanying beautiful restoration, by 

 Dr E. H. Traquair, of the form known as 

 Holoptychius, shows the nature of the overlap- 

 ping scales. The mosaic arrangement can be 

 studied (fig. 15 E). 



Coelacanthus, Diplurus, Undina and Macropoma 

 are four noteworthy genera, for they are all 

 highly specialised forms, having arrived at this 

 distinction chiefly by degeneration. Further- 

 more, "these have," says Dr Smith Woodward, 

 " perhaps the most remarkable range of all 

 known extinct fishes, occurring almost un- 

 changed throughout the whole series of forma- 

 tions from the lower Carboniferous to the upper 

 Chalk." Amongst other things, they are remark- 

 able for the fact that the air-bladder was ossified. 



Diplurus seems to have threatened to forestall 

 the Cheshire cat, for its body has become exces- 

 sively shortened, so that the head is relatively 

 enormous in size. It is further remarkable for 

 the fact that it, together with its cousin Undina, 

 was blessed with two tails, one behind the other 

 (see p. 56). 



Strangely enough, a few of these crossop- 

 terygian or fringe-finned fishes have survived to 

 the present day, in the "bichir," Polypterus bichir of 

 the Nile (fig. 15 E), the reed-fish (Calamoichthys 

 malabaricus) of Old Calabar. These are, further- 

 more, remarkable in that they differ from the 

 fossil forms described above in the form of 

 the skeletal elements of the pectoral fin, which 



