TnB CARBONIFEROUS AGE. 153 



appear in the Devonian, in the shallow fish-banks and 

 the Anodon-like bivalves found with fossil plants. 

 In the coal period they become very manifest. The 

 animals found in the shales with the coal are all, even 

 the aquatic ones, distinct from those of the open seas 

 of the period. Some of them may have lived in salt 

 or brackish water, but not in the open sea. They are 

 creatures of still and shallow waters. It is true that 

 in some coal-fields marine beds occur in the coal 

 measures with their characteristic fossils, but these 

 are quite distinct from the usual animal remains of 

 the coal-fields, and mark occasional overflows of the 

 sea, owing to subsidence of the land. It is important 

 to notice this geographical difierence, marking the 

 greater specialisation and division of labour, if we 

 may so speak, that was in the process of introduction. 

 The sea of the Carboniferous period presented in 

 the main similar great groups of animals to those 

 of the Devonian, represented however by diSerent 

 species. We may notice merely some of the salient 

 points of resemblance or difierence. The old types 

 of corals continue in great force; but it is their last 

 time, for they rapidly decay in the succeeding Per- 

 mian and disappear. The Crinoids are as numerous 

 and beautiful as in any other period, and here for the 

 first time we meet with the new and higher type of 

 the sea-urchin, in large and beautiful species. One 

 curious group, that of the Pentremites, a sort of larval 

 form, is known here alone. Among the lamp-shells 

 we may note, as peculiarly and abundantly Carboni- 



