74 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



of the Menevian rocks, 32 are Crustacea — the only other classes 

 fairly represented being the Brachiopoda, 6 species, and the Ptero- 

 poda, 6 species. A marked feature is the appearance of Cystidea 

 (Protocystites) and Crinoidea (Dendrocrinus). Eight whole classes are 

 entirely unrepresented : the Plantas, Hydrozoa, Actinozoa, Bryozoa, 

 Lamellibranchiata, Gasteropoda, Heteropoda, and Cephalopoda are all 

 absent. The genera that first made their appearance in the British 

 Menevian sea were Protocystites, Dendrocrinus, JSerpulites, 7 Crus- 

 tacea (Holocephcdina, Entomis, Anojoolenus, Arionellus, Leperditia, 

 Erynnis, and Carausia), Orthis among the Brachiopoda, and 2 Pte- 

 ropoda (Cyrtotheca and Stenotheca). The other genera appeared for 

 the first time in the lowest Cambrian of the St.-David's promontory. 



Table II. — Menevian. 



From the 

 Longmynd 

 rocks. 



Classes. 



Genera. 



Species. 



Pass to 

 Lower 

 Lingula. 





Plantse. 









3 





1 



4 



i 





Hydrozoa. 











Actinozoa. 













1 



1 









3 



3 





3 

 4 



Crustacea 



12 



32 



1 8 4 





Bryozoa. 









3 

 4 





4 



6 



3 

 3 





Lamellibranchiata. 











Gasteropoda. 













3 



6 



1 





Heteropoda. 











Cephalopoda. 









3 





24 



52 



1 3 

 1 9 



LlNGULA-ELAGS. 



The fossiliferous strata lying both above and below the Lingula- 

 group have of late years been well described and their fossil contents 

 marked out, the fauna of each group carefully investigated, com- 

 pared, and catalogued. The Harlech and Llanberris and also the 

 Menevian beds of South "Wales have been exhaustively illustrated 

 by Hicks and Salter. Upon the Tremadoc group, in North Wales, 

 the labours of Mr. Homfray, Mr. Ash, and the late Mr. Salter leave 

 little to be done ; subsequently Dr. Hicks investigated the Tre- 

 madoc and Arenig groups in the St.-David's promontory, with what 

 success I hope to show. It must not be forgotten that since the 

 Geological Survey (thirty years ago) mapped much of North and 



