94 
Guide to Arachnida. 
Sub-order II.— OPISTHOTHELAE. 
The spinning appendages in the members of this sub-order are 
situated at the posterior end of the abdomen, just in front of the 
anus. All trace of the tergal plates of the abdomen has been lost, 
and remnants only of the ventral plates are to be found protecting 
the pulmonary sacs. 
To the Opisthothelae belong all existing spiders (with the 
exception of Liphistius and Anadiastothele), and the majority of 
those found fossilised in the gypsum or amber-beds and lacustrine 
deposits of the Miocene and Oligocene periods in Europe and 
North America. 
Tribe i.— Mygalomorphae. 
In the spiders belonging to this group the posterior pair of 
biramous spinning appendages are usually alone retained. The 
basal segment of the first appendage projects forwards, the fang 
closing backwards upon it. Two pairs of pulmonary sacs are 
present. 
This group contains the bird-eating spiders (“ Mygale ”) and 
trap-door spiders and their allies, which are nearly all confined to 
the tropical or warmer temperate regions. There are a number 
of families, the more interesting of which are briefly described 
below. 
Eam. — Aviculariidae. 
The spiders of this family have the tips of the legs and the 
under surface of the terminal joint (or joints) of the legs furnished 
with a dense pad of iridescent hairs. Digging spines are not 
present on the chelicerae. 
The large, hairy spiders, which are commonly known as 
“ Mygale ,” or bird-eating spiders, belong to this family. A West 
Indian species (Psalmopoeus cambridgi ) is sometimes found con- 
cealed in the bunches of bananas which are imported into this 
country. Some of the South American species ( Theraphosa , 
Xenesthis) reach a very large size, and are the largest known spiders. 
They are nearly all tropical forms. So far as is known, none of them 
spin regular snares; many of them, however, construct a silken 
funnel at the entrance to their nests. In an allied family, the 
Dipluridae, the entrance is surrounded by a large flat web, which 
