19 J 3- CARFKNTKR — T/ie /risk Specie.^ of Pctrobhis. 229 
paired processes (gonapophyses or paramera) on both the 
eighth and ninth abdominal segments in the male, Petrobius 
has these structures on the ninth segment only, not on 
the eighth. Verhoeff has pointed out that in his Haloma- 
chilis — undoubtedly congeneric with Petrobius — the feelers 
have no scales except on the two basal segments, the apex 
of the mandible is untoothed (figs. 2, 3, II., III., a) and the 
tip of the labial palp (fig. 7, VII.) is beset with numerous 
flattened sensory spines (figs. 7, a, VII., a.). From the genus 
Praemachilis, Grassi, to which belong most, if not all, of 
the Irish inland insects of this family, Petrobius may be 
easily distinguished by the presence of two pairs of exsertile 
vesicles (figs. 5, V., ve) on each abdominal segment from the 
second to the fifth inclusive. In species of Praemachilis 
these segments have each only one pair of these vesicles. 
Petrobius brevistylis, sp. nov. 
(PLATE 2). 
Length (body and tail process) 21 mm. Feelers as long 
as body (11 mm.) general aspect and colouring as in P. 
maritimus : the whole body covered with dark scaling ; 
feelers, cerci, and tail-process white-ringed. Paired ocelli 
dumb-bell shaped, less than a transverse diameter apart 
(fig. 1,0). Median ocellus sub-ovate transverse (fig. i, m 0.) 
Mandible with blunt apex (figs. 2, 3a). Maxilla with lacinia 
shorter than galea (fig. 6) ; palp having its six elongate 
segments with proportional lengths 6: 6: 8-5: 8-5: 6; 
segments of palp relatively thicker than in P. maritimus and 
the antepenultimate markedly swollen distally. Eighth 
abdominal sternum with subcoxae produced into prominent 
rounded lobes (fig. 8). Ninth abdominal sternum (fig. 9) 
with sub -coxae produced into very small pointed processes ; 
stylets relatively short and thick, with very short, blunt apical 
spines ; gonapophyses with slightly sinuate outer edges 
reaching to the tips of the sub -coxae. Penis very elongate 
projecting beyond the stylets. Ovipositor of female nearly 
as long as the cerci, which are less than half the length 
of the tail-process. 
Locality, Portraine, Co. Dublin. 
