MESOZOIC AGE 



JURASSIC PERIOD 



SPONGES THE annals of marine invertebrate life, if humble, were not 

 uneventful. Sponges were in great force. Some six-rayed 

 forms now had their needles arranged into a highly complex 

 network (Craticularia) ; and among the four-rayed some 

 thick-walled, cylinder-shaped forms of modern type were 

 making their appearance (Cylindrophyma). 



CORALS Corals do not seem to have made much headway during 

 the early part of the Period ; but in the course of its long 

 years, reef-building corals both perforate and non-perforate 

 became more abundant than ever. In central Europe, a 

 very large part of which was submerged, they seem to have 

 spread far and wide over the sea-floor. 



Some new non-perforate forms were in the seas with cups 

 divided up with numerous partitions in the manner of a 

 fungus-cap (Fungidce). These and other families, first known 

 in this Period, have persisted until the present time (Stylo- 

 phoridce, Turbinolidce). 



SEA-LILIES Crinoids or " Sea-lilies/' after a somewhat chequered 

 career ever since the close of the Silurian, were now reviving. 

 Modernised forms, such as had appeared in the Trias, seem by 

 this time to have practically superseded all the older-fashioned 

 types. No trace has been found of sanitary reformers, con- 

 spicuous in earlier times with cumbrous waste-pipes. 



Some of the fixed sea-lilies, hitherto confined to the shal- 

 lows, were at this time spreading out into comparatively 

 deep waters (Eugeniacrinus). Forms free and stemless at 

 least in the adult state were certainly on the increase 

 (Antedon, etc.). At the same time there were stemless 

 crinoids which apparently had no desire for a free life. 



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