i68 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



described by Dr. H. "Woodward, and the only one known from the 

 Woolhope beds of Little Hope. Lituites cornu-arietis. Sow., and 

 Orihoceras conicum, Sow., although not ranging higher than the 

 Woolhope beds, appeared in the Llandovery, and help to connect 

 the Lower Wenlock with the Upper and Lower Llandovery. In 

 the Denbighshire Grits we have almost unexpectedly 3 genera and 

 7 species, only 2 of which are of Llandovery age (Orthoceras tenui- 

 cinctum, Port!., and 0. subgregarium, M'Coy). The remaining 5 

 species pass from the Denbighshire rocks, where they are first known, 

 to the Upper Wenlock ; they are 0. primcevum, Forbes, 0. tracheale, 

 Sow., 0. ventricosum, Phragmoceras nautileum, and Cyrtoceras ibex. 

 26 of the 30 species occur in the Wenlock Limestone and Shale ; 13 

 range through South Wales, and 12 through North Wales, 7 belonging 

 equally to North and South Wales. The only 3 Irish species known 

 are Orthoceras (Creseis) primcevum, Forbes, 0. subundulatum, Portl., 

 and 0. tenuicinctum, Portl. ; and the 3 Scotch forms are 0. Madareni, 

 Salt., 0. subundulatum, Portl., and 0. tenuiGinctum, P ortl. 11 species 

 pass to the Lower Ludlow; 2 of these, and the only 2 known 

 (Lituites giganteus, Sow., and Orthoceras angidatum, Wahl.), pass 

 to the Aymestry Limestone ; and 3 genera and 8 species range to the 

 Upper Ludlow ; thus only 4 genera and 9 species out of the 30 

 are really Llandovery, or these 9 species come up from the Llan- 

 dovery and Caradoc. 



The accompanying Table shows the numerical history of the 14 

 classes. The first four columns illustrate the stratigraphical distri- 

 bution of the species through the Tarannon beds, Denbighshire 

 Grits, Woolhope beds, W T enlock Shales and Limestone, indeed all the 

 formations above the Upper Llandovery. The succeeding five 

 columns show the geographical distribution of the species through 

 North Wales, South Wales, Westmoreland, Scotland, and Ireland ; 

 and to show still further the connexion between the Wenlock and 

 Ludlow fauna, I have stated in the remaining or last three columns 

 the number of species that pass to the three divisions of the Ludlow 

 group, in which it will be seen that out of the 171 genera and 536 

 Wenlock species, 71 genera and 126 species pass to the Lower 

 Ludlow, 38 genera and 52 species to the Aymestry, and 51 genera 

 and 87 species to the Upper Ludlow; any higher transgression from 

 the Ludlow into the Devonian is given under the Ludlow table. 

 There are only 20 species, including the 6 Fishes from the passage- 

 beds and the 8 species of Merostomata, that range through the 

 Ludlow series. The oldest fish-remains occur in the Lower Ludlow, 

 Scaphasjois ludensis, Salt., being the oldest species known. 



