ARACHNIDA. EURYPTERIDA 



345 



they are divisible into two groups — the anterior segments 

 being short and broad, whilst the posterior are long and 



Fig. 148. Ventral surface of Pterygotus osiliensis, from the Upper 

 Silurian, Rootzikiill. a, epistome ; b, metastoma ; c, first pair of 

 appendages (chelicerae) ; d, compound eyes ; /, I., genital oper- 

 culum ; g, tail-plate or ' telson ' ; V — 5', second to sixth pairs of 

 appendages ; I. — V., ventral plate-like appendages of the mesosoma ; 

 7 — 12, segments of the metasoma. Reduced. (After Schmidt.) 



narrow. The six anterior segments of the abdomen bear 

 appendages and form the mesosoma (fig. 148, I. — v. ; fig. 



