406 ME. J. C. HAWKSHAW ON THE 



US but little, althougli eveu here the links which unite S. hirimdi- 

 nacea of South America with S. antarctica of New Zealand, by- 

 way of the Southern Ocean, are very interesting. The distribu- 

 tion of the Skuas or Parasitic Grulls seems also clearly to con- 

 nect the northern and southern hemispheres by way of the 

 Pacific. It is, in fact, easier to specify the isolated groups which 

 liave Qio apparent connexion with the Pacific, foremost amongst 

 which is that comprising the New-Zealand L. iulleri and L. sco- 

 pidinus, the Australian L. novce-liollandice, and the South- African 

 L. liartlauhi. In the Arctic region there are the two isolated and 

 specialized genera of Grulls, Pagophila and JRhodostethia, which are 

 not known on the Pacific side ; whilst amongst the Terns the in- 

 tertropical genera Nmnia, Anous, and Gygis, although somewhat 

 related inter se, offer no particular points of union with the typical 

 Sternince. It is admitted that the present record is necessarily 

 very imperfect, but it seems to me that the bulk of the evidence 

 indicates the North Pacific as the centre of dispersal ; and whether 

 this view be accepted or not, I trust that the points to which I 

 have drawn attention may at least show that Mr. A. E. "Wallace's 

 statement that the Laridce are of little use in the study of geogra- 

 phical distribution is capable of a slight modification. 



On the Action of Limpets {Patella) in sinking Pits in and 

 Abrading the Surface of the Chalk at Dover. By J. Clabke 

 Hawkshaw, M.A., FG.S. (Communicated by Dr. J. Mtjrie, 

 P.L.S.) 



[Kead April 18, 1878.] 



(Abstract.) 



The surface of the chalk which is exposed between high- and 

 low- water mark on the foreshore to the east of Dover is covered 

 by a series of small and finely grooved hollows made in the sub- 

 stance of the chalk. These abrasions of the surface are made by 

 the limpets when feeding on the coating of delicate seaweed which 

 covers the surface of the chalk. 



When the rock has a good coating of this seaweed, the pro- 

 ceedings of any single limpet may be well seen. The lingual 

 teeth make a small scoop or groove in the chalk ; and as the 

 animal makes a number of grooves one beside the other, a line is 

 produced. After the limpet has completed a line, which is curved 



