i 3 o AMERICAN SPIDERS 



Sheet-Web Atypical Tarantulas. It is of particular interest that 

 among the atypical tarantulas we should find a group that parallels 

 very closely the sheet-web tarantulas of the family Dipluridae. 

 The hind spinnerets of these spiders are greatly elongated (par- 

 ticularly the terminal segment, which is flexible) and rather widely 

 spaced; this is probably an adaptation for spinning the sheet web, 

 and it illustrates how in widely unrelated creatures similar activities 

 often lead to the production of similar morphological features. The 

 resemblance between Hexura and the diplurids is an amazing one. 

 We find it running over a silken sheet web as do its distant relatives. 

 Were we not deterred by what appear to be more fundamental 

 features, we would ordinarily place them close together, perhaps 

 deriving one directly from the other. 



As in most atypical tarantulas, six spinnerets are present, and the 

 one-jointed anterior lateral pair is much reduced in size. The 

 distance between the spinnerets and the anal tubercle is not so great 

 in Hexura as in Antrodiaetus, but this can be attributed to the mi- 

 gration of the spinneretts back and to the side a frequent occur- 

 rence in the Dipluridae. The abdomen is provided at the base with a 

 large brown tergite. The chelicerae entirely lack a rake or digging 

 instrument such as is developed in the folding-door tarantulas. The 

 palpus of the male has a well-developed conductor of the embolus, 

 and the whole organ closely resembles that of the other atypical 

 tarantulas. 



First found in the state of Washington, the typical species is 

 Hexura picea, a dusky-brown spider about one-fourth inch long. 

 It lives under leaves, trash, and pieces of wood or back on the 

 ground in pine woods, there building a loose sheet web in which 

 it stays and over which it runs. The male has long projecting 

 chelicerae armed with prominent spines. A second species of Hex- 

 ura, which differs chiefly in its paler coloration, has been reported 

 from northern California. 



The genus Mecicobothrium, on which the family name Meci- 

 cobothriidae is based, is represented by a single known species in 

 Peru. 



Folding-Door Tarantulas and Their Kin. Except for Ac cat y ma 

 of Japan, a little-known genus that may be the same as our better- 

 known Antrodiaetus, the members of the family Accatymidae are 

 exclusively American. Two species are known to come only from 

 California: the turret spider Atypoides, and Aliatypus, which covers 



