TRILOBITES AND OTHER FOSSIL CRUSTACEA. 201 



among the fossil Crustacea on account of their singular 

 interest and beauty ; but nearly all other living groups 

 of this family are represented in the fossil state. We 

 have some occurring in the latter condition which 

 have long been extinct, as the Eurypteridce, for 

 instance. Its members were both abundant and huge 

 of size during the Upper Silurian and Devonian 



Fig. 161. Recent Entomostracan (magnified"). The upper figure shows the two 

 valve-like parts of the crust. 



periods. Specimens of this group may be seen in 

 nearly all our British museums. The Phyllopoda were 

 among the first crustaceans to appear in the early seas, 

 and were represented by Hymenocaris. The Ento- 

 mostraca are the lowest organized among this varied 

 class of animals, and from the Lower Silurian rocks 

 upwards and onwards into the seas, lakes, and rivers 



