- “eS 
THE SEA-DRAGONS, 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, 
Primevel Dragons, Fish Dragons, and Serpent Dragons. 
The Primeval 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 Ichthyosauriaa 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 
