414 



NORTH AMERICAN INDEX FOSSILS. 



29. S. lacoanus Claypole. (S. excelsior ¥[2i\\.) (Fig. 1715.) Devonic. 



Form as shown in figure; surface of cephalon covered with 

 conspicuous squamiform tubercles, elongated and much elevated 

 over anterior part of cephalon, broader and more triangular pos- 

 teriorly. 



Catskill of New York; Chemung of Pennsylvania. 



Fig. 1714. Hugh^nilleria socialis, Fig. 1715. Stylonurus lacoanus, ixovc\ 

 dorsal view of a specimen below aver- a model by C. E. Beecher, of a specimen 

 age size. (After Sarle.) nearly five feet long. (After Beecher.) 



Subclass Arachnida. (Spiders, Scorpions, etc.) 

 The Arachnida are terrestrial animals, their respiration being 

 carried on by lung-books or tracheae. The cephalothorax is usually 

 without dorsal indications of segments, but there are six pairs of 

 cephalothoracic legs surrounding the mouth, at least four of which 

 are used for walking purposes. The abdomen is unsegmented and 

 anchylosed with the cephalothorax in the mites and ticks (Acari, 

 Tertiary-Recent), but segmented in the false scorpions (Che- 



