32 FAMILY 



Other hand, was a cover on the slate-roof principle ; — thert 

 was in some of tlieir genera about one- third more of each 

 scale covered than exposed ; and this is so rare a ganoidal 

 mode of arrangement, that, with the exception of the Dip- 

 terus, — a genus which, though it gives its name to the Dij)- 

 terian sept, differed greatly from every other Dipterian, — 1 

 know not, beyond the limits of the ancient Celacanth family^ 

 a single ganoid that possessed it. The bony covering of the 

 Celacanths was farthest removed in character from shagreen, 

 as that of their contemporaries the Acanths approximated to 

 it most nearly : they were, in this respect, the two extremes 

 of their order ; and, did we lind the Celacanths in but the 

 later geological formations, while the Acanths were restricted 

 to the earlier, it might be urged by assertors of the develop- 

 ment hypothesis, that the amply imbricated slate-like scale 

 of the latter had been developed, in the lapse of ages, from the 

 shagreen tubercle, by passing in its downward course — broad- 

 ening and expanding as it descended — through the minute, 

 scarcely imbricated discs of the Acanths, and the more amply 

 imbricated tile-like rhombs of the Dipterians and Palseonisci, 

 until it had reached its full extent of imbrication in the fa- 

 miliar modern type exemplified in both the Celacanths and 

 the ordinary fishes. But such is not the order which nature 

 has observed ; — the two extremes of the ganoidal scale appear 

 together in the same early formation ; both become extinct 

 at a period geologically remote ; and the ganoidal scales of the 

 existing state of things which most nearly resemble those of 

 ancient time are scales formed on the intermediate or tile- 

 roof principle. 



The scales of the Celacanths were, in almost all the genera 

 which compose the family, of great size, — in some species, of 

 the greatest size to which this kind of integument ever at- 

 tained. Of a Celacanth of the Coal Measures, the Holop- 

 tychius Hibheriif the scales in the larger specimens were oc- 



