LIFE 509 



in tlu- aspect of the fishes, and (9) the great sea-serpents, 

 t'rom land-reptiles. 



(1) The ammonites were represented by many beautiful forms 

 ( IMS,'. 428). They deployed along ascending lines in most cases, but 

 erratic and degenerate tendencies showed themselves. Despite 

 these adverse foreshadowings, the ammonifies were still in the 

 heyday of their luxuriance and beauty. 



(2) Another division of cephalopods, the belemnites, had appeared 

 in the Trias, and rose to prominence rapidly. They are represented 

 in the fossil state chiefly by their internal shell or "pen" (Fig. 429). 



Fig. 429. The internal shell of a bchmnitc, restored; the lower, solid, conical 

 portion (ni the lelt in the Fig.), the part most commonly preserved, is the rostrum 

 or k'uard; the middle portion is the pfiragmocotte, which is a diminutive chambered 

 shell with septa, siphuncle, and protoconch as in the older tetrabranch order; the 

 upper part is the prostracum, which corresponds to the "pen" of living cuttle-fish. 



In the course of the period the belemnites came almost to rival the 

 ammonites, and were almost as characteristic of the successive 

 stages of deposition. The first known cuttle-fishes also appeared 

 at this time. 



(3) Pelecypods flourished during the period (Fig. 430), and, took 

 on a markedly modern aspect, the oyster family taking the lead. 

 Gastropods were abundant in some places, but singularly absent 

 in others. Existing genera were represented. 



(4) Suggestive of shallow clear seas was the reappearance of 

 corals and crinoids in abundance in the later part of the period. 

 The modern type of corals (Hexacoralla) was in the ascendant and 

 formed reefs, especially in European seas. Crinoids also rose again 

 to prominence, though their diversity was not great. Most of them 

 lived in shallow water, as most of the Paleozoic types had; but there 

 is evidence that deep-water species had appeared, leading toward 

 the prevalent 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. 



