42 Proceedings of the Royal Physical Society. 



care and skill she has displayed in the preparation of the 

 drawings. I am also indebted to the Council of the Marine 

 Biological Association for accommodation at their Plymouth 

 Laboratory during the examination of certain of the South 

 Polar Collections. 



Eeferences. 



Eights, J., " Description of a New Animal belonging to the 

 Arachnides of Latreille, discovered in the sea along the 

 shores of the New South Shetland Islands," Boston Jour. 

 Nat. Hist., vol. i., 1837, pp. 203-6. 1 Plate. 



Hodgson, T. V., "On a new Pycnogonid from the South Polar 

 Regions," Ann. and Mag. Nat. Hist., ser. 7, vol. xiv., 

 1904, pp. 458-462. 1 Plate. 



VIII. The Black-hacks of the Bass. By William Evans, 

 r.R.S.E., M.B.O.U. 



(Read 19tli December 1904.) 



It has long been known that a small colony of Herring 

 Gulls {Larus argentatus, Gmel.), and a few Black-backed 

 Gulls, annually make their nests on the grassy slopes near 

 the summit of the Bass. But, whereas the ornithologists 

 who visited the Rock during the first half of last century 

 seem all to have regarded the Black-backed Gulls they 

 observed breeding there as Great Black-backs {Larus 

 marinus, Linn.), only Lesser Black-backs (Lanes fuscus, 

 Linn.) have been found by those who have carefully 

 examined the birds in recent years. In fact, the breeding 

 of L. fuscus on the Bass was proved, as we shall see, some 

 forty years ago. The question thus raised is, Has there been 

 a change of species, or were the older naturalists wrong in 

 their identification ? The point is of considerable import- 

 ance, for, if it could be established beyond doubt that no 

 mistake was made, it would show that formerly the breeding- 

 range of the Great Black-back on the east coast of Britain 

 extended much farther south than it now does. So far 

 as I know, L. marinus has, at the present time, no breeding- 



