until after all the great sub-kingdoms of invertebrates have been long in existence; and there is no reason for thinking that future discoveries will materially affect the _relative_ order of succession thus indicated. LITERATURE. From the vast and daily-increasing mass of Silurian literature, it is impossible to do more than select a small number of works which have a classical and historical interest to the English-speaking geologist, or which embody researches on special groups of Silurian animals--anything like an enumeration of all the works and papers on this subject being wholly out of the question. Apart, therefore, from numerous and in many cases extremely important memoirs, by various well-known observers, both at home and abroad, the following are some of the more weighty works to which the student may refer in investigating the physical characters and succession of the Silurian strata and their fossil contents:-- (1) 'Siluria.' Sir Roderick Murchison. (2) 'Geology of Russia in Europe.' Murchison (with M. de Verneuil and Count von Keyserling). (3) 'Bassin Silurien de Bohême Centrale.' Barrande. (4) 'Introduction to the Catalogue of British Palæozoic Fossils in the Woodwardian Museum of Cambridge.' Sedgwick. (5) 'Die Urwelt Russlands.' Eichwald. (6) 'Report on the Geology of Londonderry, Tyrone,' &c. Portlock. (7) "Geology of North Wales"--'Mem. Geol. Survey of Great Britain,' vol. iii. Ramsay. (8) 'Geology of Canada,' 1863. Sir W. E. Logan; and the 'Reports of Progress of the Geological Survey' since 1863. (9) 'Memoirs of the Geological Survey of Great Britain,' (10) 'Reports of the Geological Surveys of the States of New York, Illinois, Ohio, Iowa, Michigan, Vermont, Wisconsin, Minnesota,' &c. By Emmons, Hall, Worthen, Meek, Newberry, Orton, Winchell, Dale Owen, &c. (11) 'Thesaurus Siluricus.' Bigsby. (12) 'British Palæozoic Fossils.' M'Coy. (13) 'Synopsis of the Silurian Fossils of Ireland,' M'Coy. (14) "Appendix to the Geology of North Wales"--'Mem. Geol. Survey,' vol. iii. Salter. (15) 'Catalogue of the Cambrian and Silurian Fossils in the Woodwardian Museum of Cambridge.' Salter. (16) 'Characteristic British Fossils.' Baily. (17) 'Catalogue of British Fossils.' Morris. (18) 'Palæozoic Fossils of Canada.' Billings. (19) 'Decades of the Geological Survey of Canada.' Billings, Salter, Rupert Jones. (20) 'Decades of the Geological Survey of Great Britain.' Salter, Edward, Forbes. (21) 'Palæontology of New York,' vols. i.-iii. Hall. (22) 'Palæontology of Illinois.' Meek and Worthen. (23) 'Palæontology of Ohio.' Meek, Hall, Whitfield, Nicholson. (24) 'Silurian Fauna of West Tennessee' (Silurische Fauna des Westlichen Tennessee). Ferdinand Roemer. (25) 'Reports on the State Cabinet of New York.' Hall. (26) 'Lethæa Geognostica.' Bronn. (27) 'Index Palæontologicus.' Bronn. (28) 'Lethæa Rossica.' Eichwald. (29) 'Lethæa Suecica.' Hisinger.