422 SPECIAL GEOLOGY. 



and that of Worcestershire, the beautiful 

 (fig. 178). 



Another thin band of fissile limestone, which traverses 

 the upper lias has afforded likewise the remains of 

 Neuropterous and other insects, so that the two zones of insect 

 limestone, which bound as it were the great liasic group of 

 England, contain the remains of beautifully preserved air- 

 breathing articulata, thereby attesting the proximity of dry 

 land to the ocean which was tenanted by the colossal saurians. 



Crustacea belonging to the genus Coleia and minute 

 shells supposed to be Cyproida are found in the lower lias of 

 the Vale of Gloucester, and from the same stratum two 

 species of Astacus have been obtained. 



EEPTILES or THE LIAS. The most marvellous of all the 

 remains intombed in the lias, are the marine Saurian reptiles, 

 belonging to the family Ichihyosauridce ; the genera with 

 which we are best acquainted, are the Ichthyosaurus and the 

 Plesiosaurus. 



THE ICHTHYOSAURUS (from ixQvs, fish, and o-avpa, a lizard) 

 like its congener, the Plesiosaurus, is remarkable for 

 uniting such combinations of structure as are now distributed 

 through various classes of animals, but which no longer 

 exist in any one. Thus it possessed the snout of a porpoise, 

 the teeth of a crocodile, the head of a lizard, the sternal 

 arch of the OrnitJiorhynchus, the paddles of a whale, and the 

 vertebra of a fish. Its general outline is considered to have 

 most nearly resembled that of the porpoise. The teeth are 

 numerous, sharp, conical, and striated, resembling those of a 

 crocodile ; they are also supplied by replacing teeth, in the 

 same manner as in that saurian. The eye was of enormous 

 magnitude, and the sclerotic or outer coat was encircled by 

 a series of thin bony plates, as in chelonia and in some birds, 

 especially the golden eagle, an arrangement which gives an 

 immense extent and power of vision. The sternum and collar 

 bones resemble in structure those of the Ornithorhynchus, the 

 construction in both creatures being intended to adapt them 

 for an aquatic life. The two fore-paddles were large, and 

 composed of about one hundred bones, while the hinder pair 

 are smaller, consisting only of thirty or forty. The vertebra 

 are biconcave, like those of fishes. Of this genus ten species 

 are known in the lias. 



