igo 



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 

 Ftn-ygotus (Fig. 164)' 

 and Huglimilleria ^ it is 

 semi-ovoid. The lateral 

 eyes are at the margin 

 of tlie carapace in Ptery- 

 gotus, Slimonia (Fig. 165, 

 a), and Huglimilleria, but 

 in the other genera, in- 

 cluding the earliest form, 

 Stra'bojys,^ 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 

 _,,,„, , .,. . c.v -11 TT are represented as having 



Fig. 164. — Pterygotus osiliensis, bcnmidt, Upper '- _ ° 



Silurian, RootzikuU, Oesel. Ventral surface, a larger number of joiutS. 



and 



Reduced. (After Schmidt.) 1-6, Appendages of TT„]jUp Ti^vrijnfprii'i 



the prosoma; 7-12, niesosoma ; 7, 8, genital '-'"^"^« J-^tmypimuS 



operculum; 13-18, metasoma ; 19, tail - plate ; Ptei'ygotus, the SeCOnd 

 rt, epistome ; 6, metastoma ; c, coxae of .sixth • c -\ ■ 



pair of appendages. P^ir of appendages m 



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 Purypterus the fifth pair of appendages are 

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



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

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



