PUZZLES AND PATRIARCHS. 205 



the shagreen denticles of the head had become 

 fused so as to form a number of separate bony 

 plates for the protection of the skull. The 

 denticles of the body had become modified to 

 form a closely fitting mosaic of diamond-shaped 

 pavement-like scales. The teeth were few in 

 number and degenerate in type. The peculiar 

 type of fin, not only as a whole, but also on 

 account of the disappearance of distinct support- 

 ing rays, must also be regarded as degenerate 

 in form. This early specialisation led to their 

 speedy extinction, without leaving direct des- 

 cendants. 



