252 THE SCOTTISH NATURALIST 



Adrien Dollfus, from the Tyrol, with which it agrees in all 

 structural characters, only differing slightly in the colour 

 markings. I am indebted to the kindness of Professor 

 D'Arcy Thompson, F.R.S., for the loan of these and many 

 other continental species. 



Hitherto the distribution in the British Isles of this 

 species has been as follows : Essex, 1898. This record 

 rests upon the identification of Canon Norman, who 

 examined specimens received from Mr W. M. Webb, and 

 states : " They were only young specimens, but seem clearly 

 referable to P. ratzeburgii." l Personally, I regard the record 

 as a doubtful one. In 1912 2 I received this Woodlouse 

 from near King's Norton, Worcestershire, and in 1917 3 from 

 Darwen, Lancashire. Examples received from St Helier, 

 Jersey, in 19 13, which I then regarded as referable to this 

 species, I have, in the light of further knowledge, re-examined, 

 and now consider them to be immature examples of 

 P. rathkii. Finally, I have quite recently received three 

 not quite fully grown specimens from Mr J. Williams 

 Vaughan, which were collected at Tenby, Pembrokeshire. 



To anyone not acquainted with the continental species 

 of this genus, P. ratzeburgii is a most difficult one to identify, 

 but the striking difference in the length of the proximal 

 joint of the flagellum of the antenna, which is only about 

 half of that of the distal joint, at once serves to differentiate 

 it. The almost semicircular median cephalic lobe is also 

 a well-marked character, but this is frequently approached 

 by specimens which are undoubtedly referable to P. rathkii. 

 Further, it may be pointed out that the lateral cephalic 

 lobes of P. ratzeburgii are always narrowly rounded at the 

 tip and slope inwardly, whereas in P. rathkii they are more 

 truncate terminally. This character has been very accurately 

 figured by Carl, 4 who, however, minimises the median lobe 

 of the latter species. 



1 Ann. Mag. Nat. Hist., 1899 (s. 7), vol. iii. 



2 Journ. Econ. Biol., 1913, vol. viii., p. 17. 



3 Lane, and Ches. Nat., 19 17, p. 307. 



4 Monog. Schiveis. Isopoden, 1908, t.v,, fig. 120, 121. 



