THE AGE OF INVERTEBRATES OF THE SEA. 83 



formations with little more than specific change — presenting in 

 this a strange contrast to the Trilobites. While the latter were 



Fig. 78. — Devonian and Carboniferous Trilobites. 

 a, Phaceps lat'frons (Bronn). b, Philipsia Howi (Billings) (tail). 



still flourishing, about the close of the Lower Silurian, a 

 remarkable group of large and highly-developed creatures, 



I 0. 



Fig. 79. — Palaeozoic Ostracod Crustaceans. Magnified. 



a. Bairdia. b. Cytherella itijlata (Jones), r, Cythere. Carboniferous, d. Beyrtchia 

 yonesit (Dn). Carboniferous, e, Beyric/tiupustulosa{iia.\\). Upper Silurian. 



allied to the Trilobites, but suited for rapid swimming rather 

 than creeping, was introduced ; and in the Upper Silurian and 



G 2 



^h 



