Distribution of the Rhabdophora. 

 Table VI. {continued). 



359 



A cursory examination of the Table given above is sufficient 

 to convince those who accept the data already brought forward 

 of the total distinctness in palseontological features between 

 the Graptolite faunas of the Bala and the Arenig. In the 

 true Bala beds here cited not a single example of the families 

 of the Dichograptidae or Phyllograptidas has hitherto been 

 detected. So far as our present information enables us to 

 judge, they appear to have become wholly extinct ; and their 

 place is occupied by the very distinct families of the Diplo- 

 graptidee and Dicranograptidse. The Diplograptidse, so 

 feebly represented in the Arenig and Lower-Llandeilo rocks, 

 are now the dominant forms. In every zone they occur in 

 swarms, and of the two genera Diplograptus and Climaco- 

 graptus it is doubtful which is the more prolific. The old 

 genus CryptograptuS) however, which is by no means rare in 

 the highest Arenig, and the individuals of which teem in the 



