32 4 



Proceedings of the Royal Irish Academy. 



ultimate slightly swollen apically. Eighth abdominal sternum (fig. 8), with 



sub-coxae not produced into rounded lobes. Ninth abdominal sternum (fig. 9), 



with sub-coxae produced into pointed processes ; stylets slender and elongate, 



terminating in a prominent spine nearly half 



the length of the appcnelage. Gonapophyses 



unannulated, not nearly reaching the apex 



of the sub-coxa, beyond which the tip of 



the penis projects but slightly. Ovipositor 



of female nearly as long as the cerci, which 



are half as long as the median terminal 



appendage of the abdomen. 



The above characters will serve to 



differentiate this insect from our other 



Irish species. In the latter the paired 

 ocelli are almost in contact, the median 

 ocellus is sub-ovate, the apex of the 

 mandible is rounded, the lacinia of the 

 maxilla is markedly shorter than the galea, 

 and the palp, less slender than in P. mari- 

 timus, has its six elongate segments pro- 

 portionally as 6 : 6 : 85 : S - 5 : 6. With a 

 little practice the two species can be 

 distinguished as to this character by means 

 of a hand-lens. More important, however, 

 are the differences in the eighth and ninth 

 abdominal segments and their appendages. 

 In the other species, the stylet of the ninth 

 segment in both sexes is relatively short, 

 and its spine inconspicuous and stumpy. 

 The sub-coxa of the ninth segment is drawn 

 out into a very short acuminate process; 

 but that of the eighth segment is pro- 

 duced into a prominent rounded lobe as 

 in Oudemans' species. The gonapophyses 

 reach beyond the tip of the sub-coxa, and 

 the penis beyond the extremity of the 

 stylets. 



Silvestri has lately (1911) described several new species of Petrobiua 

 from North America, placing them in a sub-genus Pedetontus, which he 

 distinguishes by the absence of the characteristic rounded lobe on the sub- 



Petrobius maiutimus. 

 . Eighth abdominal segment of male 

 ventral aspect: *., sternum; s.c, 

 sub-coxa ; St., stylet. 

 . Ninth abdominal segment of male 

 ventral aspect, s.c, sub-coxa; 

 g., gonapophysis ; p., penis. 

 Magnification of figs. 8 and 9 = 36. 



