1 SEGMENTATION 289 
and of a pair of long pointed pieces which project on to the next 
segment. Just as in the case of the genital operculum the basal 
part is united in front to the appendages, the remainder being 
free, and separating the greater part of the two plate-like append- 
ages. In the complete animal the median process of this segment 
is covered by the median process of the genital operculum. The 
remaining appendages of the female, and all the appendages 
behind the operculum in the male, are without any median 
ath 
ri 1 1) 
uhh ae i 
TA ST 
l 1 
Fia. 
Wurypterus fischeri, Hichw. Upper Silurian. (After Holm.) A, Genital 
operculum of male; @, median process. B, Middle part of second appendage of 
the mesosoma in the female, showing the median process, 
process, and the plates of each pair unite by a suture in the 
middle line. 
The metasoma (Fig. 161, 13-18) consists of six segments 
which become longer and narrower from before backwards. Each 
segment is covered by a ring-like sheath or sclerite, and bears no 
appendages. The posterior end of the last segment is produced 
into a lobe on each side, and between these phe: the long, narrow 
tail-spine arises (Fig. 161, 19). 
The other genera of the Eurypterida do not differ in any 
important morphological respects from the form just described, 
VOL. IV U 
