20 Annals Entomological Society of America [Vol. XV, 



genital cavity; and there is no trace of styli. The inner surface 

 of the sternum is covered by a much folded glandular epithelium. 

 The cerci are not modified as claspers, and are longer, flexible, 

 with long hairs and sensillae, although unsegmented. There 

 is a small external cereal basipodite. In all these respects they 

 are approached by the Tettigoniid subfamily Rhaphidophorinae. 

 The anal plates are generally more prominent and heavily 

 chitinized than in the Tettigonoidea. The supra-anal plate 

 is undivided and is sometimes, as in GryUus and Nemobiiis, 

 indistinctly separated from the tenth tergum. 



More important characters are found in the genitalia 

 (q. V.) 



Tridactyloidea. The outstanding characteristics of the 

 males of this group, apart from the penis, are the weakening 

 and infolding of the posterior abdominal terga, particularly 

 those of segments 8, 9 and 10, which are more or less concealed 

 by the overlapping 7th tergum, the dorsal lengths of segments 

 8 and 9 being greatly reduced by the obliquity of their hind 

 margins; the styliform and sometimes two-jointed cerci, the 

 long moveable processes of the paraprocts and the absence of 

 true styli.* 



In TridactyliLS apicaUs Say the terga are mesially grooved 

 with steeply sloping sides, and the 9th is divided and concealed 

 by the 8th, except towards the lateral margins. The 10th is 

 much larger but is likewise divided by the median groove, 

 and the supra-anal plate is also sulcate with only the lateral 

 margins strongly chitinized. The paraprocts are chitinized 

 and bear a pair of slender, styliform processes, like those of the 

 female. The sterna are wider than the terga, the 9th forming 

 a flattened and undivided hypandrium. 



In Ripipteryx the general characteristics of the terga are 

 similar but with marked variations according to the species. 



* Crampton ('20d) considers these stj'liform appendages as probably true 

 styli, belonging to seg. 11, the paraprocts representing the coxites of that segment. 

 If these processes were true styli we should expect to find them in some other 

 groups of Orthopteroid insects besides the Tridactylidae, as well as in the Thy- 

 sanura, in which styli sometimes occur on nearly all of the abdominal segments. 

 It is noteworthy, however, that even in such Thysanura as Alacliilis, in which the 

 styli are seen in their most primitive and best developed condition, they are 

 absent from the 10th segment and paraprocts. The development of styliform 

 processes in connection with the genitalia is very common in insects and the 

 presence of these processes in this single small group of Orthoptera is an 

 insufificient basis for speculation as to their origin. 



