156 



PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



are sparingly and irregularly distributed ; but we should expect this 

 from the habits and habitats of 3 at least of the genera. No less 

 than 36 species come up from the Lower Llandovery (22 of the same 

 are Caradoc) ; and 41 of the 65 range into the Wenlock beds. As 

 among the Crustacea, few species belong to the Upper Llandovery 

 proper, showing how slight is the evidence afforded us to separate the 

 Lower and Upper Llandovery. The stratigraphical unconformity is, 

 however, completely borne out by a corresponding palseontological 

 break. This is most decisively seen from the Actinozoa, the 

 Crustacea, the Brachiopoda, and the Lamellibranchiata ; indeed Car- 

 diganshire has as yet only yielded 1 species of Actinozoa, Petraia 

 elongata, M'Coy. The Upper Llandovery rocks of the nine chief 

 areas given below have yielded the following number of genera and 

 species of Brachiopoda : — 



Co unties. 



Grenera. 



Species. 



Pembrokeshire 



11 



19 



Caermarthenshire 



12 



38 







none. 



Radnorshire 



6 



22 



Gloucestershire 



9 



27 



Worcestershire 



11 



35 



Shropshire 



13 



13 





9 



12 





10 



19 



No less than 11 genera and 41 species pass up to the Wenlock 

 group, thus showing that a greater number of species in this class 

 pass up than belong to any even of the most prolific areas. 



Lamellibranchiata. — Considering the few species known in the 

 Lower Llandovery (3), we have here a marked change in the greatly 

 increased fauna of bivalve Mollusca, which have increased from 

 the 3 genera and 3 species of the Lower Llandovery (Pterincea retro- 

 flecea, Mytilus mytilimeris, and OrtJionota sulcata) to 12 genera and 

 29 species. 2 of the 3 species above named pass to these upper beds, 

 so that the specific fauna is essentially new ; in the end, however, 

 it gives to the Wenlock 7 genera and 15 species ; or 50 per cent, 

 pass to the Wenlock. The Worcestershire area is most prolific, 

 12 species occurring. Only 3 species are known in Scotland, 

 Anodontopsis bulla, Pterincea Soiuerbyi, and Cardiola striata, and 3 

 in Ireland, Anodontopsis bulla, M'Coy, Pterincva bidlata, M'Coy, 

 and Ctenodonta subcylindrica, M'Coy. No species is known either 

 in Radnorshire or Caermarthenshire. ( Vide Table No. XII.) 



Gasteropoda. — Equally balanced with the above group, the dis- 

 tributional value being through species of Holopella, Acrocidia, JRlia- 

 phistoma, and Turbo. These species, too, have a wide geographical 

 distribution, Worcestershire, as before, possessing the greatest num- 

 ber of species (9), although here only equal to Ireland, which has 

 also 9 species ; while Caermarthenshire has 7, the remainder of 

 the 13 genera and 28 species being equally distributed. 6 genera 

 and 8 species pass to the Wenlock; they are Aeroculia haliotis, 



