ORDOVICIAN SYSTEM : NAUNGKANGYI STAGE. 



97 



the formation with its equivalents in other regions until more was known 

 about the stratigraphical conditions actually prevailing in the field. 



Although much remains to be done in working out the details 

 of the stratigraphy, — the determination, for 



toIogki e revicLnco Palai0n " instance > .of the exact horizon of the unique, 

 though richly fossiliferous, Cystidean beds of 

 Sedaw being still uncertain, — the division of the formation (leaving 

 out of account for the present the Ngwetaung sandstones, which 

 have so far not yielded any determinable fossils) into two easily 

 distinguished groups, a lower and an upper, has been established ; 

 and I propose to review the palseontological evidence placed at our 

 disposal by Mr. Cowper Keed's able Memoir, in the light of the 

 more complete stratigraphical knowledge we possess. 



In order to make this evidence more clear, it will be convenient 

 to arrange the fauna described from each divi- 

 Range and distribu- s [ on 0 f the formation respectively in tabular 

 species,. form, giving the stratigraphical position of 



each genus and species, or its nearest allies, as it has been deter- 

 mined in other regions. In these tables new species are printed 

 as before in heavier type, and those which are found in both the 

 upper and lower stages of the formation are marked with an 

 asterisk : — 



