THE UPPER SILURIAN PERIOD. 133 



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- 

 organized, 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 impossible to do more than select a small number of works 

 which have a classical and historical interest to the English- 

 speaking geologists, 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 and Europe. ' Murchison (with M. 



de Verneuil and Count von Keyserling). 



(3) ' Bassin Siluren de Boheme Centrale. ' Barrande. 



(4) ' Introduction to the Catalogue of British Palaeozoic Fos- 



sils in the Woodwardian Museum of Cambridge. ' 

 Sedgwick. 



(5) ' Die Urwelt Russlands. ' Eichwald. 



(6) ' Report on the Geology of Londonderry, Tyrone, ' &c. 



Portlock. 



(/) "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 State of New 



York, Illinois, Ohio, Iowa, Michigan, Vermont, Wis- 

 consin, Minnesota, ' &c. By Emmons, Hall, Worthen, 

 Meek, Newberry, Orton, Winchell, Dale Owen, &c. 

 (n) * Thesaurus Siluricus. ' Bigsby. 



