344 



ARACHNIDA. EURYPTERIDA 



Behind the prosoma come the twelve free and movable 

 segments of the abdomen ; in Pterygotus (fig. 147) these 



^ 



^^~s&~^d- 



Fig. 147. Dorsal surface of Pterygotus osiliensis, from the Upper 

 Silurian, Rootzikiill. c, first pair of appendages (chelicerse) ; d, com- 

 pound eyes; e, simple eyes; g, tail-plate or 'telson'; 5', sixth pair 

 of appendages of prosoma ; 1 — 6, segments of the mesosoma ; 7 — 12, 

 segments of the metasoma. Reduced. (After Schmidt.) 



segments gradually decrease in width in passing from the 

 anterior to the posterior end, but in many cases (fig. 149) 



