PERMIAN PERIOD 67 



was thus terminated by the decided predominance of the 

 latter. 



Ammonoids — the most recently developed cephalopods ammonoids 

 — were exhibiting all the adaptability of young life. Gonia- 

 tites were disappearing, or at least, by an increased porta- 

 bility of the shell, were being transformed into ammonites. 

 This is evidenced by the twisted and complicated patterns 

 which were now being wrought beneath the sheU-surface 

 (Medlicottia, Xenodiscus). Outward ornamentation of the 

 shell was also becoming a feature. 



Trilobites — so widespread and varied in the past — were trilobites 

 now represented by only one or two species that soon became 

 extinct (Phillipsia). Sea-scorpions were also but feebly sea- 

 represented {E. temipes) ; and likewise vanished in the scorpions 

 course of the Period. To redress the balance some very small 

 creatures, developing apparently in the direction of lobsters crustaceans 

 and crabs, were now beginning to appear (Hemitrochi- 

 schus). 



Marine invertebrate life may not, of course, have suffered 

 so greatly as the geological record leads one to surmise ; and 

 discoveries may yet be made which wiU point to its having 

 been in a much less impoverished condition. There is, 

 however, good reason to suppose that in some regions, 

 especially in the southern hemisphere, Permian life for the 

 most part laboured under exceptional difficulties. At the 

 commencement of the Period, and more or less until its close, 

 severe glacial conditions prevailed over vast areas, that had 

 for long enjoyed mild and equable climate ; and the results 

 to life must have been disastrous. 



Vegetation, without doubt, was greatly affected ; and vegetation 

 some growths, long accustomed to humid and relaxing airs, 

 having lost their pristine powers of ready adaptation, were 

 in a parlous state. The progress, however, of growths of 

 newer type and of more elasticity was, it would seem, 

 expedited. 



Calamites or " horsetails " certainly suffered ; and the 

 branching tree-Uke club-mosses, and their pillar-hke aUies 

 dwindled almost to extinction (Lepidodendra, SigillaricB). 

 The endeavour of certain Carboniferous lycopods to steal a 



