THE JURASSIC PERIOD. 85 



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

 dominant but not exclusive habit. 



(5) The long, slow evolution of the echinoids in the Paleozoic era 

 was succeeded in the late Trias by the beginning of a rapid and strong 

 evolution in the form of sea-urchins, and these were now on their 

 rapidly ascending curve which reached its climax in the early Tertiary. 

 The Jura was especially rich in the so-called " regular f> sea-urchins 

 (Cidaroida and Diadematoida) . The cidarid type, with large club- 

 shaped spines, was characteristic (Fig. 360, e). 



(6) The crustacean dynasties of the Paleozoic, the. trilobites in 

 the sea and the eurypterids in the land waters, now quite extinct, 

 were succeeded by the decapods which rose to a moderate and pro- 

 longed ascendency* The prawns and lobsters (Macroura, long- 

 tailed decapods) were the earlier division, and the most numerous 

 in the Jura, but the first of the known crabs (Brachyura, short-tailed 

 decapods) appeared in this period. The macrourans seem to have 

 especially frequented embayments and protected locations near the 

 land or perhaps within the land, such as are represented in the famous 

 Sole nh of en deposit, where terrestrial, fresh- water, and marine forms 

 are preserved in the same sediments. It is not improbable that the 

 macrourans, then as now, had representatives in the terrestrial as well 

 as marine waters. 



(7) Sponges were very prolific and well preserved, and give char- 

 acter to the Spongiten Kalk of the Upper Jura. Foraminifera flourished 

 and were well preserved, a foreshadowing of their great importance 

 in the Cretaceous period. Radiolarians furnished, by their siliceous 

 tests, the material for the flints that abound in certain parts of the 

 system. 



The brachiopods retained the Terebratula-Rhynchonella aspect they 

 had assumed in the Trias, but were no longer a leading feature in the 

 fauna except locally. 



(8) A marked change in the aspect of the fishes had set in during 

 the Trias, and was continued with further development in the Jura. 

 The crossopterygians and dipnoans were greatly reduced; the sela- 

 chians continued with undiminished numbers; the skates and rays 

 began their modern career by appearing in two typical families (Squati- 

 nidcc, Fig. 361, and Rhinobatidce) ; the Chimceridce, the existing family 

 of sea-cats or spook-fishes, made its appearance and developed notably 



