THE PENNSYLVANIAN PERIOD. 



613 



tain amphibious insects, and doubtless of many unknown forms. 

 Aside from the developments of the fresh-water fish and of the amphib- 

 ians, which have already been sufficiently emphasized, perhaps the 

 most suggestive feature was the association of the arthropods with 

 other forms of life. Eurypterids were still in existence, and their 

 relics are so intimately associated with beautifully preserved ferns, 

 calamites, insects, spiders and scorpions as to leave no reasonable 

 doubt that they were true fresh-water forms. In the more notable 

 localities, as at Mazon Creek, Illinois, and Cannelton, Pennsylvania, 

 the fern fronds were preserved with al- 

 most perfect fidelity, and without the 

 coiling, crumpling and shredding that 

 would inevitably have attended trans- 

 portation for i any ,, .notable distance. At 

 the famous locality on Mazon Creek, un- 

 crumpled fronds form the centers of thou- 

 sands of concretions (Fig. 277), and 

 insects, spiders, scorpions and eurypterids 

 form the centers of others associated with 

 them. All must have been fossilized 

 with a minimum of transportation, and 

 under the most quiet conditions. Almost 

 equally instructive is the association at 

 Cannelton, shown in Fig. 285, though the 

 vegetation is more fragmentary. A not- 

 distant relative of the eurypterids was 

 present in the beautiful Prestwichia 

 dance (Fig. 284, I), whose resemblance 

 to the trilobites on the one hand, and to the king crabs on the other 

 is rather striking, and probably implies a remote ancestral relationship. 

 There were also malacostracans, resembling cray-fish, but referred J to 

 a separate order (Fig. 284, f), and other crustaceans of shrimp-like 

 appearance (Fig. 284, k). Taken together these show a very inter- 

 esting deployment of the arthropods, and if this be considered in con- 

 nection with the peculiar association of the eurypterids, ostracoderms, 

 and fishes, of the Devonian and late Silurian, it is not without sug- 

 gestiveness in connection with the views of Patten (p. 482) relative 

 to the genetic relations of the arthropods and vertebrates, and of Cham- 



Fig. 235. — Natural association- 

 of Eurypterus mansfieldi with 

 ferns and calamites. (From 

 Dana after Hall.) 



