MEROSTOMATA. 



551 



second post-cephalic shield, which is terminated by the movable, 

 spine-like telson. The only genus of this family is Limulus itself, 

 the characters of which have been already treated of in some detail. 

 The earliest undoubted fossil species of Limulus appear in the Trias 

 of Europe, and other representatives of the genus are found in the 

 Jurassic rocks (the Lithographic Slates of Germany), and in the 



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Fig. 415. — Earypterus Fischcri, from the Silurian rocks of Oesel, viewed from above and re- 

 stored, the size being about one-fifth of nature. The segments behind the carapace are numbered, 

 the first six being sometimes considered as thoracic. (After Friedrich Schmidt. Copied from 

 Zittel.) 



Cretaceous and Tertiary deposits. Of the existing species of the 

 genus, one is found on the east coast of North America, and others 

 occur on the eastern shores of Asia and in the Malayan Archipelago. 

 Order II. Eurypterida. — The Eurypterids are large Crusta- 

 ceans (fig. 415), in which the body is elongated and compressed, and 

 the chitinous integument is ornamented with a characteristic scale-like 



