290 



ARACHNIDA EURYPTERIDA 



All the genera, of which about thirteen have been recognised, 

 are placed in one family. 



Fam. Eurypteridae. The carapace varies somewhat in out- 

 line ; in Slimonia it is more distinctly quadrate than in 



Eurypterus, whilst in 

 Pterygotus (Fig. 164) 

 and Huglimilleria * it is 

 semi-ovoid. The lateral 

 eyes are at the margin 

 of the carapace in Ptery- 

 gotus, Slimonia (Fig. 165, 

 a), and Hughmilleria, but 

 in the other genera, in- 

 cluding the earliest form, 

 Strabops? they are on the 

 dorsal surface at a greater 

 or less distance from the 

 margin. 



The pre-oral append- 

 ages of Pterygotus (Fig. 

 164, i) differ from those 

 of other genera in their 

 much greater length and 

 in the large size of the 

 chelae ; they probably 

 consist of a proximal 

 joint and chelae only, 

 although, commonly, they 



are represented as having 

 FIG. 164. Pterygotus osiliensis, Schmidt, Upper 



Silurian, Rootzikiill, Oesel. Ventral surface, a larger number of joints. 



Reduced. (After Schmidt.) 1-6, Appendages of Unlike Eurypterus and 



the prosoma ; 7-12, niesosoma ; 7, 8, genital *" 



operculum ; 13-18, met.isoma ; 19, tail - plate ; Pterygotus, the Second 



^tr5Si4r^^ ; ^~^ - *^ of appendages in 



Slimonia (Fig. 165, 2) 



differ from the third, fourth, and fifth pairs in being distinctly 

 smaller and more slender, and it is probable that they were 

 tactile. Whilst in Eurypterus the fifth pair of appendages are 

 larger than the three preceding pairs, and also differ from them in 



Sarle, New York State Museum, Bulletin 69, Palaeont. 9, 1903, p. 1087. 

 2 Beecher, Geol. Mag. 1901, p. 561. 



