ANNIVERSARY ADDRESS OF THE PRESIDENT. 



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The preponderance of species in one genus, as in Aviculopecten, 

 is unexampled in any other British formation. 150 species occur in 

 Britain and Europe ; 50 have been described from America, and all 

 differ from our forms. The species occurring in the Belgian Car- 

 boniferous rocks are known to us through the researches of De 

 Xoninck. In Ireland, mainly through the researches of H'Coy 

 and Baily, the Integropallialia appear to have been exhaustively 

 recorded. The genus Avimla, in the Irish Carboniferous rocks, 

 numbers about 23 species, Aviculopecten 80, Pecten 5, Pteronites 5, 

 Posidonomya 8, Pterincea 3, Pinna 5. Scotland : Avicula 10, Avicu- 

 lopecten 50, Pinna 4, Posidonomya 2, Pteronites 6. England : Avi- 

 cula 16, Aviculopecten 48, Pinna 5, Posidonomya 8, Pteronites 3, and 

 Pterinata 1. These comparisons are important, as showing geogra- 

 phical distribution as well as age. The collective fauna illustrating 

 this group in all Europe beyond Belgium does not exceed 50 species, 

 showing either want of research or the small development of the 

 Carboniferous rocks east of Khenish Prussia. 



Lamellibranchtata. — Dimyaria*. — No less than 43 genera and 

 245 described species occur in the Carboniferous rocks, the largest 

 number being in the Carboniferous Limestone (30 genera and 182 

 species); the underlying Lower Limestone and Shales yield 23 genera 

 and 103 species ; and the Calciferous beds of the north of England 

 and Scotland 17 genera and 38 species ; only 9 species are Yoredale. 

 Many species are necessarily common to the three lower horizons ; 

 but the faunal contents are as stated. The Coal-measure species will 

 be noticed in their place. 



Thus the united British Lamellibranchiate (or Pelecypod) fauna 

 numerically reaches 54 genera and 424 species, 179 being Mono- 

 myarian Asiphonida (Integropallialia) and 245 Siphonida (Sinu- 

 pallialia). Hitherto I have not mentioned the Coal-measure Dimy- 



* 18 families, including the Arcidse, Trigonidse, and Unionidse. 



