524 
W. P. PURCELL. 
simple form of the external sexual organs, the presence of 
four spiracles, etc. 
The remarkable genus Liphistius, which I have had no 
opportunity of carefully examining, appears, as Pocock (’92) 
has pointed out, to be much more primitive than the rest of 
the group, at least in some of its characters. One of the most 
interesting among these is the mesial position of the spinners 
on the under side of the abdomen, so that in this genus 
none of the ventral abdominal segments have been exces- 
sively elongated (text-fig. 1). Considering the apparently 
primitive structure of this genus, which has also its abdomen 
Tkxt-pig. 1. — Abdomen of Liphistius (after Pocock, ’92). 
Tkxt-fig. 2. — Abdomen of a mygalomorphous spider. 
ec. t. 8 and 9. Depressions in the integument to which the ventral 
longitudinal muscles are attached at the posterior margins of 
somites 8 and 9 g. o. External genital opening. IV., lb". 
First and second pair of lung-books, sp'., f^p". Spiracles of the 
first and second pair of lung-books. 7 — 11 denote the extent 
of the seventh to eleventh somites. 
segmented dorsally like a Pedipalp, it is somewhat peculiar 
that both respiratory segments (judging from the figures 
and descriptions given by Simon and Pocock) evidently 
possess a deep interpulmonary or epigastric fold, like the 
Pedipalpi and the Aranese verm. 
In the rest of the group (Pocock’s Mygalomorphm) the 
fourth abdominal (tenth post-oral) segment has greatly 
1 
2 
