ANNIVERSARY ADDRESS OF THE PRESIDENT. 



73 



poda in the Menevian beds. The first two are confined to this 

 horizon ; S. fistula passes to the Upper Lingula-flags. 



Crustacea. — The largest crustacean fauna of the six divisions of 

 the lowest Cambrian rocks occnrs here. 12 genera and 32 species 

 characterize the Menevian beds both of North and South Wales. 

 Agnostus is represented by 7 species, Anopolenus by 3, Conocoryphe 

 by 7, Paradoocides by 3, Holocephalina by 2, and Leperditia by 4 

 species. These 6 genera are the chief and most largely represented. 

 Arionellus, Erinnys, Microdiscus, and Carausia, each with one species, 

 are confined to the Menevian beds, and generically characterize them. 

 The black slaty flags of St. David's yield the gigantic Paradoocides P. 

 aurora, Salt., P. Davidis, Salt., and P. Hicksii, Salt.; this last-named 

 species has been recorded from the Lingula-flags of North Wales under 

 the name P. Forclihammeri. 14 of the 32 species pass to the Lower 

 Lingula-flags, bnt none higher ; and the Menevian beds are con- 

 nected below with the Harlech beds and the Longmynd group 

 through 4 species only, viz. Agnostus cambrensis, Hicks, Conoco- 

 ryplie bufo, Hicks, Paradoocides aurora, Salt., and P. Hicksii, Salt. 

 No Oleni occur in the Menevian rocks, although 13 species belong 

 to the Lingula-flags proper. Olenus is essentially an Upper Lingula- 

 flag genus, 9 species occurring in that series ; and none pass out of 

 the Lower Cambrian rocks or above the Tremadoc group, where 

 4 species occur (0. alatus, 0. impar, 0. triarthrus, and 0. Salteri). 



Bryozoa. — No remains of this class occur in the Menevian ; they 

 first appear in the Upper Lingula-flags under the form oiDictyonemal 



Brachiopoda. — Only 4 genera and 6 species range through the 

 Menevian beds, Or this HicJcsii, Salt., being the only peculiar form. 

 Lingula ferruginea, Salt., and var. ovalis, Hicks, Obolella maculata, 

 Hicks, Discina pileolus, Hicks, and Orthis sagittalis, M'Coy, are asso- 

 ciated either with the Harlech beds below or the Lower Lingula beds 

 above. Every species occurs in the St.-David's Menevian beds. It 

 is not until we rise into the Llandeilo and Caradoc rocks that the 

 class becomes numerically so distinguished and important a factor 

 in the Cambrian or Silurian rocks. 



Laiiellibranchiata. — No form known in the Menevian beds. 



Gasteropoda. — No vestige known in the British rocks of this age. 



Pteropoda. — Cyrtotheca hamula, Hicks, Stenotheca cornucopia, 

 Salt., Theca corrugata, Salt., T.penultima, Salt., T. menevensis,$alt., 

 and T. stiletto, Salt., or 3 genera and 6 species, are known. 4 of 

 the 6 species are Menevian only, viz. 0. hamula, S. cornucopia, 

 T. menevensis, and T. stiletto. T. corrugata is the only form that 

 passes to the Lower Lingula-flags above. 



Heteropoda. — None known in the Menevian of either South or 

 North Wales. 



Cephalopoda. — No species has yet occurred in the British rocks 

 of this horizon, the only two species in the Lower Cambrian being 

 those before mentioned, Gyrtoceras proecox and Orthoceras sericeum, 

 both of which are Tremadoc. 



Thus we see that, out of the 52 species that constitute the fauna 



