SUCCESSION OF ANIMALS AND PLANTS. 149 



are entirely foreign to others. Tins limitation is conspi- 

 cuous with reference to entire classes among Vertebrata, 

 while, in other types, it relates more to the orders or to 

 the families, and extends frequently only to the genera or 

 the species. But, whatever be the extent of their range 

 in time, we shall presently see that all these types bear, 

 as far as the order of their succession is concerned, the 

 closest relation to the relative rank of living animals of 

 the same types compared with one another, and to the phases 

 of the embryonic growth of these types in the present 

 day, and even to their geographical distribution upon the 

 present surface of our globe. I will, however, select a few 

 examples for further discussion. Among Echinoderms 

 the Crinoids are, for a long succession of periods, the only 

 representatives of that class; next follow the Starfishes, 

 and next the Sea-Urchins, the oldest of which belong to 

 the type of Cidaris and Echinus, followed by the Clypeas- 

 troids and Spatangoids. No satisfactory evidence of the 

 existence of Holothurise has yet been found. Among 

 Crustacea, a comparison of the splendid work of Barrande 1 

 upon the Silurian System of Bohemia with the paper of 

 Count von Miinster upon the Crustacea of Solenhofen, 2 and 

 with the work of Desniarest upon fossil Crabs, 3 will at 

 once show that, while Trilobites are the only Crustacea of 

 the oldest palaeozoic rocks, there is found in the Jurassic 

 period a carcinological fauna entirely composed of Ma- 

 croura, to which Brachyura are added in the tertiary period. 

 The formations intermediate between the older palaeozoic 

 rocks and the Jura contain the remains of other Entomo- 

 straca, and later of some Macroura also. In both classes 



1 BARRANDE'sSyst.Silur.,q.a.,p.32. 3 DESMAREST, see Brongniart and 



2 GR. G. v. MUNSTER, Beitnige Desmarest's Hist. Nat. cl. Tril. et 

 zuv Petrefactenkunde, q. a., p. 146. Crust., q. a., p. 146. 



