26 THE STUDY OF INSECTS. 



then lets go its hold with its feet and sails away. That these 

 spiders travel long distances in this manner has been shown 

 by the fact that they have been seen floating through the 

 air at sea far from land. 



Representatives of nearly thirty families of spiders have 

 been found in the United States. But some of these fami- 

 lies include only rare species, and others are represented by 

 so few species that we cannot discuss them here. The 

 greater number of our spiders belong to the eleven families 

 described below. The following table will aid the student 

 in separating these families. 



TABLE FOR SEPARATING THE PRINCIPAL FAMILIES OF 



SPIDERS. 



A. Claw of the mandibles moving vertically; four lung-slits present. 



( Tarantulas?) p. 27 Theraphosid^e. 



A A. Claw of the mandibles moving horizontally; only two lung-slits 

 present, but with a single spiracle or a pair of spiracles also. 

 B. Eyes equal or nearly equal in size, and usually arranged in two 

 rows. 



C. Feet furnished with two claws (Fig. 28). Spiders which 

 do not spin webs for catching prey. 

 D. Second pair of legs not so long as the fourth pair. 



E. Maxillae with a concavity or furrow (Fig. 29). Spiders 



which live on the ground, p. 29 Drassid.e 



EE. Maxillae convex (Fig. 32). Spiders which live chiefly in 



silken tubes on bushes, p. 30 Clubionid^e. 



DD. Second pair of legs as long as or longer than the fourth 



pair. ( The crab-spiders.*) p. 40 THOMISID^E. 



CC. Feet furnished with three claws (Fig. 38). Spiders which 

 spin webs for catching prey. 



D. The caudal pair of spinnerets very long, and two-jointed. 

 Spiders which make irregular webs with a tube or hiding- 

 place at one side, from which they run on the upper surface 



of the web, to catch their prey. p. 30 Agalenid^:. 



DD. All of the spinnerets short. 



E. With cribellum and calamistrum. Spiders making webs 

 in which there are curled threads, or double threads. 



