\ 



450 MESOZOIC TIME REPTILIAN AGE. 



were Conifers and Cycads. Fig. 673 represents one of the Cycad 

 stumps, and fig. 672 is the leaf of a modern Zamia, which those of 

 the Mantellia probably resembled. Near "Whitby, on the sea-coast 

 of Yorkshire, and in the Stonesfield slate, fossil ferns are common. 

 No Jurassic Angiosperms are known. 



2. Animals. 



The Radiates include a number of Crinoids, mostly of the genera 

 Pentacrinus and Apiocrinus (fig. 720) ; also a variety of Corals (figs. 

 717-719), Star-fish (fig. 721), and Echinoids (figs. 694, 722, 722 a), 

 having in general a modern aspect, though of extinct species and 

 mostly of extinct genera. 



Among Mollusks there is a great variety of new forms, many 

 peculiar to the Mesozoic era. The last of the Brachiopods of the 

 Spirifer and Leptama families appear in the Lias (figs. 696-697). 

 These Leptsenas are minute species (fig. 696 a), contrasting wonder- 

 fully with the abundant and large Leptsenas of the Silurian, when 

 the family was at its maximum. The prevailing Brachiopods are 

 of the modern genera Terebratula and Rhynchonella. 



Conchifers comprise several new genera. Gryphaza, of the Oyster 

 family, having an incurved beak, commences in the Lias; and 

 Exogyra, another of the family, with the beak curved to one 

 side, begins in the Oolite. Trigonia, a triangular shell (successor to 

 Myophoria of the Triassic and Schizodus of the Permian), appears 

 in the Lias. 



The Gasteropods are represented by several new modern genera, 

 besides others that are now extinct. But the type of Cephalopods 

 especially undergoes great expansion. The genus Ammonites, of 

 Triassic origin, abounds in species (figs. 700, 701). The shell of the 

 Ammonite has the septa or partitions flat over the middle, but flexed 

 or plicated in a complex manner at the margin : in an upper view 

 of a septum it seems to be bordered by a few large holes, each of 

 which is a ramified pocket made by. the flexure of the margin. 

 The animal lived in the outer chamber of the shell ; but the mantle 

 descended into the cavities, and thus it is assisted in holding to its 

 shell. The siphuncle differs from that of the Nautilus family in 

 being dorsal. In some species the aperture of the shell had the 

 simple form in fig. 730 ; in others it was prolonged as in fig. 731. 

 Over 300 species lived in the Jurassic, besides many Nautili. 



In addition to these Cephalopods with external chambered shells 

 (Tetrabranchs or Tentaculifers, p. 156), there were also those having 

 an internal shell or bone (Dibranchs or Acetabulifers), a group 



