5 o8 



THE JURASSIC PERIOD 



features were (i) the continued dominance of ammonites 

 among the invertebrates, (2) the rise of the belemnites, (3) the 

 abundance and modernization of pelecypods, (4) the rejuvenation 

 of corals and crinoids, (5) the marked development of sea-urchins, 

 (6) the introduction of crabs and modern types of crustaceans, (7) 

 the prevalence of foraminifera, radiolaria, and sponges, (8) the 



Fig. 428. GROUP OF JURASSIC AMMONITES, a-b, Coroniceras bisulcatum 

 (Brug.), a lateral and ventral view of one of the Arietidtz; c, Deroceras subarmatum 

 (Young); d, Perisphinctes tiziani (Oppel); e, Reincckia brancoi Steinm. 



