STRIDTJLATING-ORGANS OF STEATODA, ETC. 



153 



(fig. 1, B) there are no spurs ; the inner edge, however, is undu- 

 lated, and in points becomes angulated, while a little below are 

 stiff hairs on small protuberances. The chitinous thoracic exten- 

 sion of the male is marked, on its superior surface with many 

 fine parallel transverse grooves, which are absent in the female 

 (fig. 1, C) ; while in the same position on both sexes are several 



1. 





(?o ^^^^ do 



Stridulating-organs of Steatoda ( Theridion) guttata, tf and O. • 



A. Male. View, from above, of chitinous ring or socket attached to ab 

 domen covering the union with thorax, do, dorsal surface. 



B. Ditto of the female, do, dorsal surface. 



C. View, from above, of chitinous extension of thorax ; female, do, dorsal 

 surface. 



ridges, which are less numerous in the male. It is quite likely 

 that individuals may vary in details ; but it appears that the 

 female of Steatoda guttata, Wider., has, as w T ell as the male, organs 

 adapted to stridulation. 



I have also examined both sexes of Steatoda bipunctata, Linn., 

 and find that the socket of the male is much shallower than 

 those of the male and female of the last-named species. The 

 inside of the external edge is rough, and the sides are lined with 

 a row of bristles seated on prominences ; and the only opposing 

 surface is a spinate ridge on the base of the thorax, which has no 

 chitinous extension covering the abdominal union. In the female 

 there is no trace of these organs. 



In the same paper already quoted (Trans. Ent. Soc. 1877, My- 

 gale stridulans) , Prof. Wood-Mason describes the totally different 

 sound-producing apparatus in male and female of "Mygale stri- 

 dulans" of Assam, "on the inner face of the basal joint of the 



LINN. JOTJEN.- 



■ZOOLOGY, VOL. XV. 



12 



