THE) UPPER SILURIAN PERIOD. 131 
dus, fig. 75, B), which are doubtless the bony scales of some 
fish resembling the modern Dog-fishes. As the above mentioned 
remains belong to two distinct, and at the same .time highly- 
organised, groups of the fishes, it is hardly likely that we are 
really presented here with the first examples of this great class. 
On the contrary, whether the so-called ‘‘ Conodonts” should 
prove to be the teeth of fishes or not, we are justified in ex- 
pecting that unequivocal remains of this group of animals will 
still be found in the Lower Silurian. It is interesting, also, to 
note that the first appearance of fishes—the lowest class of 
vertebrate animals—so far as known to us at present, does not 
take place until after all the great sub-kingdoms of invertebrates 
have been long in existence; and there is no reason for think- 
ing 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 im- 
possible 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 Bohéme Centrale.’ Barrande. 
(4) ‘Introduction to the Catalogue of British Paleozoic 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, Minne- 
sota,’ &c. By Emmons, Hall, Worthen, Meek, Newberry, 
Orton, Winchell, Dale Owen, &c. 
(11) ‘ Thesaurus Siluricus.’ Bigsby. 
) ‘British Palzeozoic Fossils.” M‘Coy. 
(13) ‘ Synopsis of the Silurian Fossils of Ireland,’ M‘Coy. 
) ‘* Appendix to the Geology of North Wales ”—‘ Mem. Geol. Survey,’ 
vol. iii, Salter. 
