12 Miss Anna J. Reilly on 



as long as tlie apical (as in P. oudemansi), but in the pro- 

 portion p. The gonapophyses in the male do not reach the 

 tips of the ninth abdominal subcox^, in this respect being 

 similar to those of P. oudemansi ; but the penis attains 

 to about three-fourths the length of the ninth abdominal 

 stylets. P. vecttnsis agrees with P. oudeina7isi and P. hrevi- 

 slylis in having prominent lobes on the subcoxse of the 

 eighth abdominal segment in the male. 



A synopsis of the prominent features of the four species of 

 Petrobms mentioned in this paper is given below : — 



A. Eighth abdominal segment S with sub- 



coxse not produced into prominent rounded [Leacli. 



lobes Petrohins mantimus, 



Ai. Eighth abdominal segment J with sub- 

 coxae produced into prominent rounded 

 lobes. 

 B. kStylets of ninth abdominal segment J 

 relatively short and thick, with very 

 short blunt apical spines; gonapophyses 

 reaching to tips of subcoxse. Penis 

 very elongate, projecting beyond the [Carpenter. 



stylets Petrobius brevistylis, 



Bi. Stylets of ninth abdominal segment J 

 relatively long and thin, with long acute 

 apical spines; gonapophyses not reaching 

 to tips of subcoxse. 

 C. Subcoxse of eighth abdominal segment 

 $ not produced into long pointed 

 processes. Penis in (^ attaining only 

 to half the length of the ninth abdo- 

 minal stylets Petrobius oudemansi, 



[Carpenter (=Machilis maritima, Oudemans). 

 Ci. Subcoxse of eighth abdominal t^egment 

 § produced into long pointed processes 

 about 5 length of stylets. Penis in c? 

 projecting to about | length of stylets. Petrobius vectensis,s^.ia.. 



Genus PetrOMACHILIS, nov. 



The antennae have scales only on the two basal segments 

 (PI. III. fig. la). The apex of the mandible is bluntly 

 truncated and bears on its inner margin two minute blunt 

 teeth (PL III. figs. 3 & 4). The galea of the maxilla is 

 jointed towards the base (PI. III. fig. 6). One pair of 

 exsertile vesicles is present on the first abdominal segment. 

 The abdominal segments 2-5 bear each two pairs of exsertile 

 vesicles (PI. IV. tigs. 2, 3, 4, & 5). The sixth and seventh 

 abdominal segments each bear one pair of exsertile vesicles. 

 The seventh abdominal segment has the subcoxse produced 

 into rounded lobes, much longer in the female than in the 

 male (PI. IV. figs. 7&7a). 



