26z AMERICAN SPIDERS 



in collections from Minnesota and Alberta. Tetragnatha extensa 

 has long been recorded from the New World, but all the published 

 records should be referred to a distinct species now called T. versi- 

 color Walckenaer. Only recently has true extensa been found in 

 North America. It is the same as the quite rare species that was 

 described as manitoba in 1942. Several names are stricken from the 

 list because American specimens seem at least to differ subspecifi- 

 cally from European examples. In America, Pityohyphantes has be- 

 come a whole complex of closely related but distinct species. At 

 this time it can be noted that Loxosceles rufescens, long held to be 

 virtually cosmopolitan in distribution, does not occur in the Amer- 

 icas, where instead we have many quite similar but nevertheless dis- 

 tinct species. 



Many of our spiders differ specifically and others generically 

 from those that occur in Europe, but the relationship to Palearctica 

 is nevertheless close. Neither area is noteworthy for its mygalo- 

 morph fauna, except in the extreme southern portions. In each 

 region is found the genus Atypus with species of very similar ap- 

 pearance, three in Europe and four in the eastern United States. 

 Strongly developed are such cribellate genera as Dictyna and Amau- 

 robius, with many species, and each area has two species of the 

 curious Hyptiotes, maker of a triangular snare. The Gnaphosidae 

 are remarkably developed in the temperate zone, and many species 

 of Gnaphosa, Zelotes, and Drassodes live on the ground or under 

 debris. The species of Clubiona in the northern United States be- 

 long to the same groups as those of Europe, but at the present time 

 we have recognized none of the species as being identical. The 

 crab spiders are remarkably represented by the genera Xysticus and 

 Philodromus, which are largely missing from the tropics. The run- 

 ning spiders of the genera Pardosa, Pirata, and Tarentula show a 

 parallel growth in both regions, and again almost none of the species 

 are identical. 



It is chiefly in the sedentary aerial spiders, all of which are well 

 known for their ballooning propensities, that one finds many Amer- 

 ican spiders identical with those from Eurasia; this is well shown 

 by the list of Argiopidae and Linyphiidae common to both areas. 

 If one were to name the single group largely typical of the tem- 

 perate zone, it would be the Linyphiidae. This great family, which 

 includes the multitudinous tiny forms that have modified their heads 

 in most singular ways (Erigomnae) and the somewhat larger related 

 sheet spinners (Linyphimae), has had an unparalleled development 



