SFIDElRS OF THE NEW GENUS ARCTACHAEA 
(ARANEAE, THERIDIIDAE) 
By Herbert W. Levi 
Museum of Comparative Zoology 
Harvard University 
The new spider genus Arctachaea is erected for two rare 
species from western North America, closely allied to 
Theridion, Arctachaea differs from the latter in abdomen 
shape and in structure of the genitalia. The rarity of the 
two species accounts for the belatedness of their description. 
Dr. W. J. Gertsch of the American Museum of Natural 
History and Dr. R. V. Chamberlin of the University of Utah 
have made specimens available to me. I extend my sincere 
thanks for their cooperation. 
Arctachaea, new genus 
Arctachaea (fern.) has Arctachaea pelyx as type species. 
Medium sized theridiid spiders. Carapace longer than 
wide, thoracic depression indistinct. Eyes subequal in size, 
anterior eye row procurved as seen from front, posterior 
row straight as viewed from above. Chelicerae lacking teeth. 
Sternum convex. First leg longest, fourth or second leg in 
males second in length, third shortest. Tarsal comb with 
few setae. Abdomen slightly longer than high with a distinct 
dorsal posterior hump. Colulus absent. 
Epigynum a raised area. Palpus with median apophysis 
Explanation of Plate 8 
Figs. 1-2 Arctachaea nordica (Chamberlin and Ivie) Fig. 1. Ventral 
view of chelicerae and palpus. Fig. 2. Anterior view of left chelicera. Figs. 
3-6. A. pelyx new species. Fig. 3. Left palpus, expanded (C, conductor; E, 
embolus; M, median apophysis; R, radix; Y, cymbium). Fig. 4. Female 
genitalia, dorsal view. Fig. 5. Epigynum. Fig. 6. Female. Figs. 7-11. A. nor- 
dica (Chamberlin and Ivie). 7. Female genitalia, dorsal view. 8. Epigynum. 
9, 10. Female. 11. Left palpus. Figs. 12-13. A. pelyx new species. 12. Pal- 
pus (Utah). 13. Palpus (Oregon). 
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