234 AMERICAN SPIDERS 



and along the inner edge, and cannot be moved separately. A single 

 spiracle opening into the tracheal tube is placed far back toward 

 the spinnerets, replacing the forward pair of openings of the pre- 

 vious series. The unpaired claw on the tarsi may or may not be 

 present. Several different body forms and quite different habits are 

 exhibited by the members of the five families, of which all but one 

 are known from within American borders. 



All eight eyes are retained by the members of the family Plec- 

 treuridae, which are among the most generalized of all ecribellate 

 spiders. Plectreurys closely resembles Ariadna in shape, but has 

 stouter legs. In the males, the first pair of legs is armed with a stout 

 spur at the end of the tibiae. This is similar to what is found in the 

 tarantulas, and undoubtedly serves to hold the legs or fangs of the 

 female during the pairing. These three-clawed spiders live under- 

 neath stones in our southwestern deserts. They have been little 

 studied. 



The tube and net weavers of the family Diguetidae differ from 

 their nearest relatives, the plectreurids, in having six eyes in a nearly 

 straight row, and in possessing in the male palpus a conductor of 

 the embolus. The single known genus, Diguetia, includes a number 

 of elongate spiders having bodies thickly covered with white hairs 

 to form distinctive bands, and quite long legs ringed in black. Sev- 

 eral species occur in the southwestern United States and in adjacent 

 Mexico. These spiders suspend a long, vertical, tubular retreat, 

 closed at the top and often three or more inches long, at the center 

 of a maze of threads. Favorite sites in the desert are the wide spaces 

 between the joints of prickly pears and small bush cacti. The fe- 

 males incorporate their egg sacs in the tube, laying one upon the 

 other like the tiles of a roof. Over the long, silken horn, which is 

 widest and flared at the mouth opening, are placed small leaves of 

 plants found nearby. Cocoon retreats from different areas differ 

 markedly in color, texture, and general composition. 



The false hackled band spinners of the family Loxoscelidae are 

 most closely related to the Scytodidae. Loxosceles weaves a large, 

 irregular web, the threads of which are similar to those of the 

 hackled band weavers. This spider lives under stones and bark, 

 and in caves. It is of medium size, yellow or brown, and the 

 flattened carapace has six eyes placed in a strongly curved row. 

 The legs are long, and lack the unpaired claws on all the tarsi. An 

 extraordinary feature is a very long process, the colulus, which is 



