172 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



in this borderland between the Upper Ludlow and the Old Red 

 Sandstone. 



Protozoa. — A series of sponges (Calcispongise) numbering 7 genera 

 and 10 species occur in the Ludlow rocks, 3 of which are also 

 Wenlock. 6 genera and 8 of the species belong to the Upper 

 Ludlow ; Amphispongia, Favospongia, and Tetragonis are new 

 forms, and appear for the first time, and, with Favospongia Buthveni, 

 Isehadites Kosnigi, and 4 species of iSpongarium, die out in the 

 Upper Ludlow. 3 genera and 5 of the species occur in the Ludlow 

 beds of Westmoreland ; they are Favospongia Buthveni, Spongarium 

 mquistriatum, S. interUneatum, S. inter ruptum, and Tetragonis Danbyi. 

 The conformable Old Eed Sandstone in the Ludlow area, or anywhere 

 along the extended strike and junction of the two formations, con- 

 tains nothing in common with the Upper Ludlow save a few fish 

 and crustacean remains, all ceasing with the Downton beds and 

 tilestones. The Eurypterids (Stylonwus megalops and Eurypterus 

 pygmceus) pass to the lower beds of the Old Red Sandstone ; but 

 through all the Old Red of South Wales (or the Silurian area) or 

 Gloucestershire or Somersetshire, from its base to its junction with 

 the Lower Carboniferous, nothing has occurred save fragments of 

 Cephalaspis and Holoptychius, no other class in the animal kingdom 

 being represented. 



Hydrozoa. — Only 1 genus and 8 species of this class seem left to 

 bring to a close the history of the Graptolite group of the Hydrozoa. 

 Monograptus has 8 species, which are all Lower Ludlow and occur 

 in the Ludlow area. In no region of the globe where the Silurian 

 rocks have been deposited have any species of this class trans- 

 gressed or passed into higher formations. About 210 species belong- 

 ing to 30 genera have lived during the Silurian epoch, ranging from 

 the Arenig with 42 species, the Llandeilo 44, Caradoc 38, Lower 

 Llandovery 50, Upper Llandovery 12, Wenlock 23, to the Ludlow 

 with 8, their maximum development being at the commencement 

 of the Lower Silurian of certain systematists. They came into 

 existence with unexampled prodigality and suddenness, but gradu- 

 ally died out as conditions grew less and less favourable for their 

 sustenance and development. America, Bohemia, Scandinavia, 

 Australia, and Britain have all largely possessed the same hydrozoal 

 fauna, illustrating the same or similar deposits. Whether homo- 

 taxially or not, most of the same genera have occurred in rocks 

 of the same age as those of the British Islands, and always under 

 the same physical conditions. The labours and researches of Hall, 

 Barrande, Geinitz, Linnarsson, Nicholson, Lapworth, Hopkinson, 

 Carruthers, and M'Coy in this field of zoological history will ever 

 reflect honour on their memory. To Mr. Lapworth graptologists 

 owe much ; no other author has given such attention to the Rhab- 

 dophora, whether we regard his specific work or that devoted to 

 their history and geological distribution through time, and his phi- 

 losophical views relative to their affinities, structure, and systematic 

 classification. 



Actixozoa. — Not a single species out of the 17 occurring in the 



