JURASSIC PERIOD. 451 



which includes very nearly all known existing species. Among 

 them the most abundant is the Belemnite. The fossil is a cylin- 

 drical stony body (fig. 670), radiated in structure, having a conical 

 cavity (or alveolus). The lower part of the cavity, in perfect spe- 

 cimens, is occupied by a small chambered cone, called the phragmo- 

 cone, which has a siphuncle. When unbroken (which is very 

 seldom), the osselet has a thin expansion above on one or two sides, 

 which is sometimes much prolonged. One form of it is shown in 

 figs. 702, 703. The Cephalopod was much like a Sepia. Fig. 732 

 represents the animal of an allied genus called Acanthoteuthis. 

 There were also species of the Sepia or Cuttle-fish family, and Cala- 

 maries, or Squids; and the ink-bags of these species (fig. 706) are 

 sometimes found fossil, and also the smaller ones of Belemnites. 

 Buckland states that he had drawings of the remains of extinct 

 species of Sepia made with their own ink. 



The sub-kingdom of Articulates is represented by various Worms, 

 Crustaceans, Spiders, and Insects ; and of the last, all the principal 

 tribes appear to have been represented, even to the highest, the 

 Hymenopters. Figs. 734, 735, are Crustaceans of the Oolite ; 733, 

 736, remains of Insects. Fig. 733 is a Dragon-fly, or Libellula (Neu- 

 ropter); fig. 736, the wing-case of a beetle (Coleopter). Fig. 737 

 is the earliest known of true Spiders, — for the only Carboniferous 

 species of the class are Scorpions. It is from Solenhofen. 



Vertebrates present no marked progress in the class of fishes : 

 there are only Ganoids and Selachians ; and none of the former 

 have vertebrated tails, this Palseozoic feature finally disappearing. 

 The Reptilian type, on the contrary, undergoes an expansion more 

 remarkable than that of Cephalopods. There are no Labyrintho- 

 donts. But the true Reptiles come forth in numerous Enaliosaurs 

 (sea-saurians, p. 346) of higher grade than the Simosaurs of the 

 Triassic, asi is shown in their solid bony skulls ; in Lacertians and 

 Crocodilians, many of which were 15 to 50 feet in length ; in great 

 Dinosaurs, the highest of Eeptiles ; in Flying Saurians (Ptero- 

 saurs), having wings much like bats ; in Turtles of several genera. 



The more common genera of Enaliosaurs are Ichthyosaurus, Plesio- 

 saurus, and Pliosaurus. The Ichthyosaurs were gigantic animals, 

 10 to 40 feet long, having paddles somewhat like the whale (fig. 

 708), long head and jaws, numerous (in some species 200) stout, 

 conical, seriated teeth, an eye of enormous dimensions, thin disk- 

 shaped biconcave vertebrae (figs. 710, 710 a). The I. communis, 

 found in the Lias of Lyme-Regis and elsewhere, was 28 or 30 feet 

 long. More than thirty species are known to have existed in the 

 Reptilian age. 



