FOSSIL SEA- MATS. 



217 



new species he has obtained by carefully washing, 

 sifting, etc., deposits likely to contain Polyzoa in 

 nearly all our British marine strata. Mr. John Young, 

 F.G.S. of Glasgow, has similarly worked the Lower 

 Carboniferous beds of Scotland, and has carefully 

 brought to light a wonderful variety. Hairmyres is 

 perhaps the best hunting-ground for these delicate 

 little fossils in Scotland, and the Halkyn Mountains 

 in Wales. But they are easiest seen on the surfaces 



Fig. 182. Polypora tuberculata, 

 showing arrangement of cells. 



Fig. 183. Diastopora Oolitical 

 a, natural size. 



of the thin dark bands of shale which frequently occur 

 in all limestones. 



The Oolitic limestones are frequently rich in 

 Polyzoa, of which perhaps Diastopora is the com- 

 monest genus, and Bidiastopora, Eschara, and Idmonea 

 the next. 



In the Chalk (a deep-sea deposit and the Polyzoa 

 seem to love clear water, as is proved by the 

 abundance of recent species on the " Gulf-weed ") the 



