34 PALAEOZOIC. 



Pentreniites, etc. Graptolites arc specially characteristic of 

 the Lower Palaeozoic rocks (Cambrian and Silurian). 



Crustacea, in the form of Trilobites, are also typical of 

 these rocks, and they extend upwards to the middle of the 

 Carboniferous series. The older genera are Asap/nis, Agnostiis, 

 Paj'ttdoxides, and TrmuclevLS ; the newer include Calyinene, 

 Homalonotus, Phacops, and PJiillipsia. Besides these, there 

 are other forms of Crustacea, the Pterygotus and Eiirypterus 

 — the former of which sometimes attained a length of five or 

 six feet. 



Brachiopoda are very abundant in some of the beds, includ- 

 ing Leptccna, Spirifer, Orthis, Prodnctus, PentanieTiis, Stropho- 

 mena ; also Mollusca of the genera Avicidopecten, Posidonomya, 

 Eiiojiiphahis, Aliuxhisojiia, Lititites, Orthoceras, Goniatites, etc. 

 The earliest known Insects in Britain make their appearance 

 in the Coal-measures,^ which have also yielded traces of 

 Myriapods and Arachnides. Fishes make their appearance 

 in the uppermost Silurian rocks — they mostly belong to the 

 Ganoid order. And so abundant do they become in certain 

 portions of the Old Red Sandstone, especially in Scotland, that 

 this period has been termed the " Age of Fishes." Amphibia 

 (Labyrinthodonts) have been met with in the Coal-measures ; 

 but no true Reptiles are known to occur in rocks older 

 than the Permian. No Mammals have been found in 

 Palaeozoic rocks. (See Synopsis of the Animal Kingdom 

 in Appendix.) 



The Palaeozoic rocks contain a few living genera of 

 Mollusca, such as Lingnla, Tcrebratula, and RJiyncJionclla. 

 As might be expected, there is no evidence of any funda- 

 mental modification or advance in the Foraminifera from the 

 Palaeozoic period to the present day.^ 



In these early periods the same groups of animals (Mollusca 

 and Crustacea) appear to have been very widely diffused, 

 suggesting that the physical conditions under which they 

 existed in Palaeozoic times were probably much more uniform 

 than they now are.^ We must also remember that the 

 Palaeozoic epoch was probably of enormous duration com- 

 pared to the succeeding geological periods. At the same 

 time we may mention that in the opinion of Sir R. S. Ball, 

 the globe was affected by enormous tides during its infancy, 



1 On the Insect Fauna of Paljeozoic rocks, see H. Goss, P. Geol. Assoc, vi. 

 271 ; and S. H. Scudder, G. Mag. 1881, 300. 



'■' Dr. W. B. Carpenter, Introd. to Study of Foraminifera (Ray Soc. ), 1862 ; 

 see also R. Etlieridge, Address to Geol. Soc. 1S81. 



•* Dr. A. Geikie, Text-Book of Geology, ed. 2, p. 21. 



