ANNIVERSARY ADDRESS OF THE PRESIDENT. 



6 7 



portance. B. multistriatus, Salt, (an Upper-Trcmadoc species), unites 

 the Heteropoda of the Lower with those of the Arenig or Middle 

 Cambrian group. 



Cephalopoda. — No form or species known until we reach the 

 horizon of the Tremadoc rocks, where for the first time we find 

 both Cyrtoceras and Ortlioceras, one species of each genus. Cyrto- 

 ceras prcecox, Salt., is, I believe, the earliest Cephalopod known. The 

 Lower Tremadoc rocks of Llanerch, west of Portmadoc, yielded the 

 Cyrtoceras ; and the Upper Tremadoc of Garth, and Llauvirn, St. 

 David's, 0. sericeum. The latter passes to the Arenig rocks. 



We have thus seen how unequally distributed (as we should ex- 

 pect) are the zoological groups through the lowest Cambrian rocks, 

 and how distinctively certain genera characterize them, and, as will 

 be found upon a separate analysis of the Menevian, Lingula-flags, 

 and Tremadoc beds, how distinct a period is represented by all below 

 and up to the close of the Tremadoc age. The six divisions of the 

 Lower Cambrian represent the earliest history of the British rocks ; 

 for out of the 61 genera and 182 species known to range through 

 them, only 11 genera and 16 species pass to the Arenig or base 

 of the Lower Silurian, or Middle Cambrian (see Table VII.). 



Table I. — Longmynd, Harlech, and Llanberris. 



Classes. 



Genera. 



Species. 



Pass to 

 Menevian. 





2? 



3? 







1 ' 



3 





Hydrozoa. 

 Actinozoa. 







Echinodermata. 











4 



4 







7 



14 



3 



Bryozoa. 





4 





3 



6 



3 



Laniellibranchiata. 





4 



Gasteropoda. 



Pteropoda 



1 



2 



1 



Heteropoda. 

 Cephalopoda. 







1 





18 



32 





Dr. Hicks has favoured me with a new classification for the 

 Lower Cambrian (Longmynd and Harlech) rocks of St. David's : 

 the geographical significance of the names employed renders them 

 of value ; and nothing of the kind has been previously attempted 

 below the Menevian group : — 



