2 ARANEIDEA. 
California, Mexico and the Central-American States, the Antilles, and the whole 
northern region of South America, gradually fading away southwards to the northern 
boundaries of Patagonia. 
It is noteworthy, however, that in both a northerly and southerly direction these 
forms follow the coast-line and spread further than they do inland, as, for instance, in 
California on the north-west and Virginia on the east, in Chili on the south-west and 
below Uruguay on the south-east coast. In this respect the area of distribution of 
the Theraphoside is almost conterminous with that of the scorpions (cf. R. I. Pocock, 
‘Geographical Distribution of Scorpions’). 
Certain groups of genera belonging to this family are, of course, still further 
restricted to the equatorial regions. For though the genus Ewrypelma extends as far 
north as Arizona, yet the genera Acanthocurria, Avicularia, Xenesthis, Sericopelma, &c. 
are not found north of Mexico, and indeed scarcely much further north than Panama. 
On the whole, therefore, we may regard the Mygalomorphe in general, and the 
family Theraphoside in particular, as essentially residents of the tropics. Certain 
forms, such as Avicularia avicularia in Brazil, and some species of Eurypelma in 
Central America, abound almost everywhere, but the majority of these huge spiders 
lurk in their dens in the depths of the primeval forest and are seldom met with. 
The first family into which the Mygalomorphe fall, the Ctenizide, comprises all 
those forms which are well known under the name “Trapdoor Spiders.” They 
construct a silk-lined burrow in the ground, closed with a hinged door at the entrance. 
‘The members of the next family, the Theraphoside, though often making a cylindrical 
burrow in the soil, make no door at the entrance. They are not artificers, as their 
structure will prove. The Ctenizide have become highly specialized in the armature of 
their legs and mandibles in correlation with their habit of digging in the soil and 
constructing carefully adjusted doorways for the protection of their domicile. The 
Theraphosidez, on the other hand, are rather specialized in the direction of rapidity 
of movement, their feet also being furnished with an exceedingly soft pad of 
claviform hairs, beautifully iridescent, which enables them to advance in stealthy 
silence on their prey, and to cross smooth horizontal surfaces with absolute confidence. 
These spiders, though they construct large cylindrical domiciles of silk in convenient 
situations, and in some genera burrow in the ground, yet make no door at the entrance, 
but rather extend the silk in an open trumpet-shaped mouth over the surrounding 
' foliage and soil. 
The third family, the Dipluride, again develop this trumpet-mouth still further, 
spreading the silk in a much wider circle over the surrounding soil or foliage, the 
snare and burrow, or tube at the back, thus assuming a very strong resemblance to the 
sheet-like snares of the family Agelenide, belonging to the section Arachnomorphe— 
a resemblance, moreover, which is not alone confined to the snares, but is even shared 
to a greater or less extent by the constructors themselves ; showing that similarity of 
