President's Address. 27 



of valves "found in pairs, and in many cases tlie similar 

 margins are turned towards each other, just as happens in 

 the Dithyrocarisr 



In 1876 the British Association met in Glasgow, and witli 

 the view of affording ^-eological visitors every facility for 

 following out their favourite pursuit, a committee of the 

 Glasgow Geological Society undertook the preparation and 

 publication of a small geological guide. This volume, entitled 

 " A Catalogue of Western Scottish Fossils, with an Introduc- 

 tion on the Geology and Palaeontology of the District," * is 

 by Messrs James Armstrong, J. Young, F.G.S., David Eobert- 

 son, r.G.S., and Professor John Young, M.D. Sufficient 

 thanks on the part of all workers interested in Scotch geology 

 cannot be accorded to these gentlemen for their disinterested 

 trouble in so readily placing before others information 

 gathered over a long series of years. In the portion relating 

 to the Silurian deposits an excellent list of fossils from 

 Girvan is given. 



The last reference I have to make to this branch of my 

 subject, is to a short paper by Mr Davidson, " Notes on Four 

 Species of Scottish Lower Silurian Brachiopoda."-|- In this 

 communication a new species of the peculiar genus Siioliono- 

 trcta is described, found by Mrs Gray in the Craighead lime- 

 stone, and named Siplwnotrcta Scotica. Two very large forms 

 of Lingula had also been met with by Mrs Gray, and these 

 Mr Davidson referred to Lingula Canadensis of Billings, a 

 characteristic shell of the Hudson Eiver group of North 

 America, and Lingida quadrata (Eichwald). The latter is a 

 Ptussian species, and it is curious to note that Siijlwnotrcta is 

 also essentially a Eussian Silurian genus. 



A final summary of the Girvan Silurian Mollusca, gathered 

 from the various papers and lists just quoted, and after 

 deducting synonyms and certain doubtful determinations, 

 yields the following numbers : 



Brachiopoda, . . . . 53 species. 

 Bivalves, . . . . 12 „ 



* Proceedings, 1876, ii., pt. 2, p. 164, Glasgow, 8vo. 

 t Geol. Mag., 1S77, iv., pp. 13-17, t. 2. 



