428 



MESOZOIC ERA— AGE OF REPTILES. 



Animals. 

 The animals of the Jurassic, marine, fresh- water, and land, were 

 very abundant, and have been well preserved. It is impossible, there- 

 fore, in the lower departments, 

 to do more than touch lightly 

 the most salient points. In 

 the higher departments we will 

 dwell a little longer. 



Corals have assumed now 

 the modern type and style of 

 partitions (Fig. 639). Among 



Fig. 637.— Cycas circinalis, x ^ v , a Living Cycad of the 

 Moluccas (after Jjecaisne). 



Fig. 638. — Stem of Cycadeoidea megalo- 

 phylla, x J. 



Echinoderms, the Crinids, or plumose-armed Crinoids, are very abun- 

 dant and very beautiful ; in fact, they seem to have reached their high- 

 est point in abundance, diversity, and gracefulness of form (Figs. 640, 

 641). But the free forms, Echinoids and Asteroids, are now equally 

 abundant (Figs. 642-644). 



Brachiopods are still abundant, though far less so than formerly ; but 

 they now belong almost wholly to the modern or sloping-shouldered 

 types, such as Terebratula and Rhynchonella. Only a very few small 

 specimens of the Paleozoic type linger until the Lias. 



Lamellibranchs, or common bivalves, are extremely abundant. 

 Among the common and characteristic forms are Trigonia, Gryphaea, 

 and Exogyra, belonging to the oyster family ; and the strangely-shaped 

 Diceras (Fig. 645). It is interesting, also, to observe here the first 

 appearance of the genus Ostrea (oyster). 



Cephalopods. — One of the most striking characteristics of the Juras- 

 sic period is the culmination of the class of Cephalopods in number, 

 diversity of forms, and, if we except some of the Silurian Orthocera- 

 tites, in size. They were represented by the Ammonites and the Be- 

 lemnites, the one belonging to the order of Tetrabranchs, or shelled, 

 the other to the Dibranchs, or naked Cephalopods. It is important to 



