158 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



or which is but dimly illuminated, would seem to be less decided transition 

 tlian ill tlie case of many other genera. Nevertheless, the facts at present 

 within possession of arancologists appear to indicate that the Tubeweavers 

 have secured no permanent representatives among our cave fauna, this 

 position being wholly occupied by members of the Retitelaria;. We have 

 tlius presented the curious fact that the species which by natural tendency 

 appear to ])C best adapted to survive cavern conditions have been thor- 

 oughly eliminated or excluded. 



