286 Annals Entomological Society of America ' [Vol. XII, 



The eighth spiracle, as in other Acridioidea, is situated in, 

 the tergite (pleuro-tergite) , but the others retain a more 

 primitive position in the pleural membrane. 



Tridactyloidea (Tridactylidae) . 



This small family has been commonly associated with the 

 Gryllidae, owing to the superficial resemblance of the typical 

 genus, Tridactyhis, to the mole-crickets (Gryllotalpinas), a 

 resemblance due to the subterranean habits of both. Thus we 

 find in both Tridactyhis and Gryllotalpa a similar form of head 

 and pronotum, short antennae, front legs adapted for digging 

 and reduction of the ovipositor, which in Tridactyhis is vestigial, 

 while in Gryllotalpa it is entirely wanting. In the Tridactylid 

 genus, Ripipteryx, however, which is not a distinctly sub- 

 terranean form, there is a well-developed ovipositor, and it is 

 not at all like that of a Gryllid, but is remarkably similar to 

 that of the Acridoidea, as suggested by de Saussure and 

 Zehntner ('94). i" These authors, however, failed to appreciate 

 fully this resemblance and made no comparisons between 

 the two groups. 



I have examined the terminal segments and ovipositor of 

 Ripipteryx for cipata Sauss. (Figs. 19-21), and find the latter to 

 be closely comparable with that of the Acridoidea, but with 

 certain important features of its own. 



The obliquity of tergites 9-11, which is slightly indicated 

 in Acrydium and associated with the weakening of the median 

 region and a breaking up of the dorsum into a number of second- 

 ary sclerites, occurs in the Tridactylidae in an exaggerated form. 

 In R. forcipata the eighth tergite is normal in shape and form 

 except that it is divided along the mid-dorsal line into two 

 lateral plates, the thin tegument between the plates being folded 

 inwards. This is also the case in a slighter degree in Acrydium. 

 The ninth tergite is also completely divided into two lateral 

 plates, but the obliquity has been carried so far that the original 

 anterior, ventral and posterior margins are respectively ventral, 

 posterior and dorsal in position. The antero-dorsal angles of 

 these plates extend forward underneath the eighth tergite 

 as two slender processes, which are apparently all there is to 

 represent the dorsal region. The tenth tergite lies dorsal to 



" Rev. Suisse de Zool., tome II, Fasc. 2, pp. 403-430, Pis. XVI, XVII (1894). 



