MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY. 211 



In the same paper I also suggested that there may be a connection 

 between hmpet-eating rats and the number of Rat Islands scattered 

 round our coasts. One such island (or islet) is attached to Herm, 

 and I have frequently disturbed Miis rattus there, but never noticed 

 any stores of its food. Another such named Rat Island is adjacent to 

 the Scillies, while another attached to Lundy Island, in the Bristol 

 Channel, has the reputation of being so called because it was the last 

 refuge of the old English black rat before its final extinction in England, 

 but that is a legend which would equally apply to every Rat Island in 

 the kingdom. 



To digress for a moment from conchological matters, Mus rattus, 

 the black or Alexandrine rat, is by no means extinct in England, 

 being still occasionally found about the London wharves and docks, 

 while at Great Yarmouth and a few other places it is comparatively 

 common. In the Island of Sark particularly Mus rattus has always 

 flourished undisturbed, and the brown or Norwegian rat has never 

 gained a footing there, probably owing to the fact that no ships call 

 at that little island. Where the brown rat does gain a footing, how- 

 ever, it invariably drives away the English black one. Nor is the black 

 rat always nor often black, though it is generally darker than our 

 ordinary brown one, from which it otherwise differs in being a smaller 

 animal, having larger and more expanded ears, with a longer and 

 more slender tail. 



Helcion pellucidum var. laevis Penn. — I have two white speci- 

 mens from Benbecula in the Hebrides. One of these is uniformly 

 conical, with the apex erect instead of drooping, which gives it a 

 deceptive resemblance to Tectura initra Esch. from the Aleutian Isles, 

 var. elongata Jeff. — Torbay, not uncommon, but always under 

 stones; Aberdeen, dead on the shore (Simpson) ! 



Tectura virginea Miill. — Mr. J. A. Hargreaves considers that 

 this species affords an instance of colour protection, at any rate at 

 Scarborough, " the protection being so marked as to render the shell 

 almost invisible even at close quarters." ^ They particulary affect 

 those rocks which are coated with a pink nuUipore, with which the 

 pink-rayed limpet harmonises marvellously ; " even an experienced 

 collector has to examine the nuUipore over and over again to obtain 

 all the specimens exposed, so completely does the background agree 

 with the shell colour," He adds that Chiton ruber l^oviQ "also occurs 

 on this nuUipore, on which it is almost invisible." 



var. lactea Jefif. — Aberdeen, very large (Simpson) ! 



Lepeta fulva var. albula Jeff. — The Minch 65f , off the Butt of 

 Lewis 99f, and Shetlands 5 if and i55f. (Simpson) ! 



I " Protective Resembla.nce in British Miiriije MoHusca ' Jotirn. of Conch., 1911, vol. xjii., 

 pp. 215-216, 



