ANNIVERSARY ADDRESS 0E THE PRESIDENT. 



177 



Extensive patches of Upper Silurian rocks on the eastern side of the 

 Silurian area and border of the Old fled, such as Woolhope, Usk, 

 the long strike of the Malverns on to May Hill, thence across the 

 Severn at Purton Passage to Tortworth, indicate great physical 

 changes in the borderland between the fossiliferous Upper Silurian 

 and the unfossiliferous Old Ked ; and whatever change brought in 

 the marine Devonian of North Devon, south of the Mendip axis and 

 on the same strike, and all the South-Wales Old Eed beneath the 

 South-Wales coal-field to the Bristol Channel, certainly must ac- 

 count for the loss of all the Ludlow species ; that the Devonian area 

 was one of long and continuous depression south of the latitude of 

 the Mendips there cannot be any doubt, and probably the mass of 

 Old Red Sandstone occupying Caermarthenshire, Monmouthshire, 

 Breconshire, Herefordshire, and Worcestershire was being at the 

 same time slowly elevated. 



Gasteropoda. — 9 genera (six of which had appeared in the 

 Wenlock) and 33 species, 11 of which were also Wenlock, range 

 through the Ludlow rocks ; the Lower Ludlow has yielded 8 genera 

 and 15 species, the Aymestry Limestone 5 genera and 11 species, 

 and the Upper Ludlow 9 genera and 21 species. 3 genera and 

 6 species occur in the Passage-beds into the Old Red Sandstone ; 

 they are Holopella conica, II. gr eg aria, Hoi op a' a ohsoleta, Mur- 

 chisonia torquata, Platyschisma helicites, and P. Williamsi. They, 

 however, cease here, none living into the red beds of the Old Red 

 Sandstone. North Wales has yielded only 2 species, Holopella 

 gracilior and H. gregaria ; Scotland only 4 species, Acroculia anti- 

 quated Euomphalus funatus, Platyschisma simulans, and P. helicites; 

 Ireland has only registered 1 species, Euomphalus alatus ; Here- 

 fordshire 7 genera and 11 species, Worcestershire 6 genera and 9 

 species, Shropshire 7 genera and 14 species, and Westmoreland 6 

 genera and 14 species. 6 genera and 13 of the 33 species come up 

 from the Wenlock and range through the Ludlow rocks ; they are 

 Acroculia, haliolis, Cyclonema corallii, G. octavia, Euomphalus alatus, 

 E. carinatus, E. funatus, E. rugosus, Holopella gracilior, H. ohsoleta, 

 Looconema elegans, L.sinuosa, Murchisoma Lloydii, and M. articulata. 

 9 species only are Lower Ludlow. All become extinct in the Tile- 

 stones and Passage-beds. 



Pteropoda. — Conularia subtilis and C. Sowerbyi, with Theca 

 Forbesii, are all the species (3) illustrating this pelagic group. The 

 two last named are Upper Ludlow. Neither the Aymestry Lime- 

 stone, Passage-beds, North Wales, or Worcestershire yield either 

 species, nor do we know of any species in Ireland. C. Sowerbyi 

 occurs in Scotland ; all 3 species in Westmoreland and 2 (Theca 

 Forbesii and Conularia Sowerbyi) in Shropshire. These last are also 

 Wenlock species. 



Heteropoda. — Bellerophon (6 species) and Ecculiomphalus Icevis 

 constitute the Ludlow stock of Heteropoda. Ecculiomphalus Icevis, 

 Bellerophon expansus and B. dilatatus occur both in the Lower and 

 Upper Ludlow. B. Murchisoni, B. obtectus, and B. trilobatus are 

 Upper Ludlow only ; 4 species occur in the Passage-beds, B. cari- 



