e 1. Mygalomorphae.--The plane of the articulation of the
appendages of the 1st pair to the prosoma (the retrovert) vertical,
the basal segment projecting straight forwards at its proximal end,
the distal segment or fang closing backwards in a direction
subparallel to the long axis of the body. Two pairs of pulmonary sacs.

Families--Theraphosidae (_Avicularia_, _Poecilotheria_). Barychelidae
(_Barychelus_, _Plagiobothrus_). Dipluridae (_Diplura_, _Macrothele_).
Ctenizidae (_Cteniza_, _Nemesia_). Atypidae (_Atypus_, _Calommata_).

[Illustration: FIG. 62.--_Liphistius desultor_. Lateral view.

I to VI, Appendages of the prosoma cut off at the base.
o, Ocular tubercle.
praegen, The prae-genital somite.
1 and 2, Sternites of the first and second opisthosomatic somites.
3 and 4, Appendages of the third and fourth opisthosomatic somites,
which are the spinning organs, and in this genus occupy their
primitive position instead of migrating to the anal region as in
other spiders.
5, Tergite of the fifth opisthosomatic somite.
11, Eleventh opisthosomatic somite; an, Anus.

(Original.)]

Tribe 2. Arachnomorpnae.--The plane of the articulation of the
appendages of the 1st pair to the prosoma horizontal, the basal
segment projecting vertically downwards, at least at its proximal end,
the distal segment or fang closing inwards nearly or quite at right
angles to the long axis of the body. The posterior pulmonary sacs
(except in _Hypochilus_) replaced by tracheal tubes; the anterior and
posterior pairs replaced by tracheal tubes in the Caponiidae.

Principal families--Hypochilidae (_Hypochilus_). Dysderidae
(_Dysdera_, _Segestria_). Caponiidae (_Caponia_, _Nops_). Filistatidae
(_Filistata_). Uloboridae (_Uloborus_, _Dinopis_). Argiapidae
(_Nephila_, _Gasteracantha_). Pholcidae (_Pholcus_, _Artema_).
Agelenidae (_Tegenuria_). Lycosidae (_Lycosa_). Clubionidae
(_Clubiona_, _Olios_, _Sparassus_) Gnaphosidae (_Gnaphosa_,
_Hemiclaea_). Thomisidae (_Thomisus_). Attidae (_Salticus_).
Urocteidae (_Uroctea_). Eresidae (_Eresus_).

_Remarks on the Araneae._--The Spiders are the most numerous and
diversified group of the Arachnida; about 2000 species are known. No
noteworthy fossil spiders are known; the best-preserved are in amber
of Oligocene age. _Protolycosa_ and _Arthrolycosa_ occur in the
Carboniferous. Morphologically, the spid