THE JURASSIC PERIOD 



715 



that deep-water species had begun to appear, leading toward the 

 prevalent but not exclusive habit of the present. 



(5) The slow evolution of the sea-urchins in the Paleozoic era 

 was succeeded in the late Trias by the beginning of a rapid evolution, 

 which reached its climax in the early Tertiary. 



(6) The Paleozoic crustaceans, the trilobites in the sea, and the 

 eurypterids in the land waters, had been succeeded by the decapods 

 which rose to a moderate and prolonged ascendancy. The prawns 



Fig. 485. JURASSIC FOSSILS, a-c, Cephalopoda: a, Cardioceras cordiformis 

 M. and H.; b, Neumayria henry i M. and H.; c, Belemnites densus M. and H. 

 d-h, Pelecypods: d, Camptonectes bellistriatus Meek; e, Mytilus whitei 

 Whitf.; /, Grammatodon inornatus M. and H.; g, Pseudomonotis curta 

 (Hall) ; h, Ostrea strigilecula White, i and /, Brachiopods: i, Rhynchonella 

 gnathophora Meek; /, Lingula brevirostra M. and H. 



and lobsters (Macrura, long-tailed decapods) were the earlier divi- 

 sion, and the most numerous in this period; but the first of the 

 known crabs (Brachyura, short-tailed decapods) appeared before the 

 period was past. The macrurans seem to have frequented embay- 

 ments and protected locations near the land, or perhaps within it, 

 where terrestrial, fresh-water, and marine species are preserved in 

 the same sediments. It is not improbable that the macrurans, 

 then as now, had representatives in terrestrial waters, as well as in 

 the sea. 



