'J 4 Guide to Arachuida. 



Sub-order II.— OPISTHOTHELAE. 



Table-case ^\\(i 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 Ijelong all existing spiders (with the 

 exception of Lijjhistms and Anacliastothele), 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 x\merica. 



Tribp: 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. 



Fam. — Aviciilariidac. 



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 coumionly known as 

 " M>/(jale," or bird-eating spiders, belong to this family. A West 

 Indian species {Psalmopoeus ccunhridrji) is sometimes found con- 

 cealed in the bunches of bananas wdiich 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 suri'ounded by a large flat web, which 



