140 



G. T. HAREIS ON THE 



two districts (Dartmoor and East Devon), one a Palaeozoic 

 semi-mountainous area of extensive peat deposits, excessive 

 rainfall and deep bogs, the other a Triassic lowland area, with 

 no peat deposits, moderate rainfall and bogs unimportant both 

 in depth and extent, would indicate that the factors influencing 

 the richness or poverty of Desmid floras must be sought for 

 elsewhere than in the geological beds upon which the habitats 

 stand, and a recent investigation of the Desmid flora of a district 

 on Eocene beds confirms this statement. It is also noteworthy 

 that the species density of the two districts is practically the same, 

 for although exact scientific methods could not be applied to 

 the field work, an approximation was made in the extent of ground 

 examined and amount of time devoted both to collecting and 

 examining the material, so that the comparison is a fairly accurate 

 one. 



COMPABATIVE TaBLE OF THE DeSMID FlOBAS OF A PALAEOZOIC 



(Caebonifebous) and Teiassic District. 



