THE JURASSIC PERIOD. 



81 



by uncoiling, spiral coiling, and other departures from the normal 

 lines of the order, presaging an episode of " sporting " and retrogression 

 in the next period, to be followed by extinction; but, despite these 

 adverse foreshadowings and some notable reduction in diversity, 



Fig. 357. — A Group of Jurassic Ammonites: a-b, Coroniceras Usulcatum (Brag.), 

 a lateral and ventral view of one of the Arietidce; c, Deroceras subarmatum (Young): 

 d, Pcrisphinetes tiziani (Oppel); e, Reineckia brancoi Steinm. 



the ammonites were yet in the climacteric stage of their luxuriance 

 and beauty. They had well-nigh reached the limits of attainment 

 in such features as close coiling, complexity of sutures, ornamenta- 

 tion and some other characteristics. The continued expansion of 

 the sea gave them still a widening field over which they spread them- 



