416 AliACIJKIDA 



the females, possessing- the palpal oi'iiaii, and often being differently 

 marked. 



Over 10,000 species are known, of which 1,300 belong in this country. 

 The order contains 2 suborders and about 2() families. 



Key to the suborders of Arcmcae: 



Oj Two pairs of lungs ; usually 2 pairs of spinnerets ; claw of mandible 



vertical in position 1. Tetrapneumones 



Ca One pair of lungs ; 3 pairs of spinnerets ; chiw of mandible horizontal in 



position, working from the side, medially 2. DiPNEUMONES 



Suborder 1. TETKAPNEUMONES. 



Often large spiders with 2 pairs of lungs and 2 or 3 pairs of spin- 

 nerets; mandibles usually project more or less forwards, the claw of 

 which projects downwards instead of transversely; with 8 eyes set 

 closely together: tropical or subtropical spiders including the bird 

 spiders and trap-door spiders; 3 families. 



Family AVICULAEIIDAE. 



Pedipalp arises near or at the tip of the maxilla, which is not dis- 

 tinct; the 4 lung spiracles covered by broad and often glistening folds: 

 40 American species. 



Pachylomertjs* Ausserer. Trap-door spiders. Cephalothorax al- 

 most as broad as long; abdomen ovoid; spinnerets 4; eyes close together, 

 on low prominences, the lateral eyes being the largest; the extremities of 

 the 2 hinder pairs of legs much thickened: 8 American species, in the 

 southern states. 



P. audonini (Lucas). Length 20 mm.; the anterior lateral eyes 

 the largest; third joint of the third pair of legs very short and crooked; 

 color glossy brown: North Carolina; the animal lives in a cylindrical 

 burrow in the ground lined with silk, the opening of which can be closed 

 by a circular door which works with a hinge. 



Suborder 2. DIPNEUMONES 



Spiders with 1 pair of lungs; tracheae also present which open to 

 the outside usually by a single spiracle; 3 pairs of spinnerets; mandibles 

 directed downwards, the claws projecting from the side towards the 

 median line: over 30 families. 



* See "A New Trap-Door Spider," by G. F. Atkinson, Am. Nat., Vol. 20, p. 583, 

 1886. 



