12 Proceedings ol the Royal Irish Academy. 



Body somewhat narrow ; thorax not markedly broader than abdomen, 

 whose tenth tergum is distinctly longer than the ninth. Bristles, simple or 

 bifid at the tip, arranged in tufts on the head, and in " combs " of two or 

 three each on the thoracic and abdominal terga. Two or three pairs of 

 abdominal stylets. 



Isolepisma bisetosa sp. nov. 



(Plate VI, figs. 71-8-2.) 



Length 7'5 mm. Feelers, median tail-process and cerci shorter than the 

 l)ody (fig. 71). Terga of thoracic segments with a "comb" of two strong 

 bristles at the hinder edge on each side of the middle line, and five or six 

 lateral "combs " (fig. 71). Terga of abdominal segments (TI-VIII, inclusive) 

 with two " combs," usually of three, but occasionally of foTir bristles at the 

 hinder edge on each side, and a comb of two bristles neai-er the median line 

 (fig. 71). Process of sub-coxa of ninth abdominal segment in both sexes 

 acuminate, nearly half as long as the stylet (figs. 80, 81). Eighth abdominal 

 segment of male (fig. 80), and seventh and eighth of female (fig. 81), with 

 short stylets. Ovipositor in female (fig. 82) elongate, projecting beyond the 

 tip of the ninth stylet for at least tlie lengtli of the latter. 



The above features serve to distinguish this species from /. trisetosa, 

 Esch. ('04, pp. 62-3, PI. I, fig. 1), which is rather smaller, has the feelers and 

 caudal process as long as tlie body, and possesses paired combs on the 

 thoracic segments consisting of three bristles each. 



Localities.— Seychelles: Bird Island (1908); He aux Eecifs (H. P. 

 Thomasset) ; Long Island (July, 1908j. Aldabra (J. C. F. Fryer, 1908-9). 

 Farquhar (30th September, 1908). Providence : Cerf Isl. (J. S. Gardiner, 

 3rd September, 1905). Amirante, Eagle Island (J. S. Gardiner, May- 

 September, 1905). 



This species is apparently abundant, as it is represented by numerous 

 examples from most of the localities. It is very closely allied to /. trisetosa, 

 Escherich— the only species of the genus hitherto known — which has 

 apparently a circumtropical range (Brazil, West Africa, Malay Archipelago). 

 1 1 may probably be regarded as having been differentiated from /. trisetosa 

 during a long period of isolation. 



Sufficient material of this species is available for an examination of the 

 principal structures of the head. The lahriim (fig. 72 Ibr) is a short, broad 

 plate, with arched front edge, hinged on to the face (fig. 72 /), which bears 

 numerous slender bristles, and two series— thi-ee on either side — of broad, 

 bifid ones, like those that project in front of the clypeus. The mandible 

 differs distinctly in shape from that of Ctenolepisma, figured by Escherich 



