PALAEOZOIC AGE 



DEVONIAN PERIOD 



Fish- LIFE now abounded not only with strange types, old and 

 new, but also with a variety of species less quaint and prob- 

 lematical. 

 OSTRACO- Sluggish flat-headed creatures in skins dotted with dentine 



DERMS were here much as those of the Silurian (Thelodus) ; and new 

 and apparently related forms were also in being. In the case 

 of the latter the scattered dentine had been collected and fused 

 into plates and scales ; and a protection resembling cuirass 

 and chain armour had resulted (Drepanaspidce). 



Shielded forms of the same character as those of the 

 previous Period were now in great force ; and, as a rule, of 

 larger size. Those, for instance, with bony head-shields 

 attained in some cases a length of two feet ; — ^twice the length 

 of the finest of their Silurian ancestors (Cephalaspidce). 



There were also some forms — rarely more than a few inches 

 long — with only remote likeness to Silurian types {Pterichthys, 

 etc.). They were fully armed with bony plates and scales ; 

 and the eyes were well brought forward as on a human face. 

 The mouth appears to have been of a primitive kind, without 

 bony jaws. The most remarkable feature of these little 

 curiosities was the possession of jointed breast fins or paddles. 

 These plated appendages were probably used for crawUng 

 as well as for swimming and balancing purposes. 



None of these shielded fish-like organisms — whatever may 

 have been the possibilities of unknown earlier and less 

 specialised forms — represented a progressive movement. In- 

 deed their total disappearance was not far distant ; for at 

 the close of the Period they all became extinct. 



Some small vertebrates, long-tailed, and with large mouths 



38 



