32 2 Proceedings of the Royal Irish Academy. 



An interesting and suggestive distributional fact is furnished by the 

 discovery of the Petrobius and three species of Collembola on the Bills 

 Bocks — a small group of outlying crags, with scanty vegetation, nine miles 

 west-north-west of Clare Island, 



THYSANUBA. 



MACHILIDAE. 



Praemachilis hibernica Carpenter. 



Machilis polypoda, Carpenter and Evans (Proc. Roy. Phys. Soc. Edinb., 

 xiv, 1899), and most British lists. 



Croaghmore cliffs, 1300 feet (A. W. Stelfox, July, 1911), one specimen. 



This species — described (1907, pp. 55-6, pi. 16) from examples taken on 

 Lambay, Co. Dublin — is now known to be generally distributed in Ireland 

 and in Great Britain. The genus Praemachilis, to which it belongs, is included 

 in a section of the family distinguished from Machilis by no abdominal 

 segment having more than one pair of exsertile vesicles : see Silvestri's 

 paper (1904, p. 5). P. hibernica is closely allied to, perhaps identical with, 

 P. italica (Grassi), from southern Europe. 



Petrobius maritimus Leach. 



Petrobius maritimus Leach (Edinb. Encycl., ix., 1809, and Zool. 

 Miscell., iii, 1817). 



Machilis maritimcc Lubbock (Bay Society Monograph, 1873), and 

 subsequent English writers (in part). 



Not M. maritima Oudemans, Beitrage, 1886. 



Nor P. maritimus Silvestri (Bedia, 1904, and Bull. Bortici, 1911). 



On all parts of the Clare Island coast above high-water mark, also under 

 stones of walls on the low cliff-tops, and along roads near the sea. In 

 outhouse of hotel (June, 1909) ; on wall above harbour and at top of eastern 

 cliffs (July, 1911); road between Glen and Kill on wayside wall (July, 

 1911). Eastern and north-eastern coast from harbour to lighthouse. 

 (B. Welch, September, 1909.) The Bills, eastern rock, 50-100 feet above 

 sea-level. (B. W., June, 1910). Wherever the species is seen, individuals 

 are numerous ; but their agility in running and leaping makes it hard to 

 capture them. 



On the mainland the species is common near the shore throughout the 

 " Clare Island District." Blacksod Bay (B. Southern, Sept., 1909). Curraun 

 Achill. (B. P. Scharff, June, 1909). Boonah (K H. Foster, May, 1909). 

 Louisburgh (N. H. P., May, 1909, and J. N. Halbert, Aug., 1910). Old 

 Head (N. Colgan). Achill. 



