Gigantostraca. 83 
Order 2.— Gigantostraca (Eurypterines). 
In the Gigantostraca the sixth (or fifth and sixth) pairs of the 
appendages of the prosoma are modified to act as paddles. There 
are twelve distinct somites in the hinder region of the body 
(mesosoma and metasoma). 
Restoration of Eurypterus fischeri (after Holm). a — Appen- 
dages of prosoma, b — Sternal plate of prosoma, c — Appendage 
believed to distinguish the female sex, perhaps an ovipositor. 
d.— Plate-like appendages of mesosoma. The first plate (which 
corresponds to two somites of the body) is the genital oper- 
culum. e — Sternal plates of metasoma. 
Table-case 
No. 19. 
