THE SEA-DEAGONS. 215 



therefore, perhaps, in conjunction with the Dipneusta, 

 branched off from the Selachii, but did not develop into 

 higher Vertebrata ; they form an extinct lateral line of the 

 pedigree, which has died out. 



The more accurately known Sea-dragons are classed into 

 three orders, distinct enough one from the other, namely, 

 PriirncBval Dragons, Fish Dragons, and Serpent Dragons. 

 The Primceval Dragons (Simosauria) are the oldest Sea- 

 dragons, and lived only during the Trias period. The 

 skeletons of many different genera of them are met with 

 in the German limestone known as " Muschel-kalk." They 

 seem upon the whole to have been very like the 

 Plesiosauria, and are, consequently, sometimes united with 

 them into one order as Sauropterygia. The Serpent 

 Dragons (Plesiosauria) lived in the oolitic and chalk 

 periods together with the Ichthyosauria. They were 

 characterised by an uncommonly long thin neck, which 

 was frequently longer than the whole body, and carried 

 a small head with a short snout. When their arched neck 

 was raised they must have looked very like a swan ; but 

 in place of wings and legs they had two pairs of short, 

 flat, oval-paddling fins. 



The body of the Fish Dragons (Ichthyosauria) was of 

 an entirely different form; these animals may be opposed 

 to the two preceding orders under the name of Fish- 

 finners (Ichthyopterygia). They possessed a very long 

 extended body, like a fish, and a heavy head with an 

 elongated, flat snout, but a very short neck. Externally, 

 they were probably very like porpoises. Their tail was 

 very long, whereas it was very short in the members of the 

 preceding orders. Also both pairs of paddling fins are 



