58 LEPIDOPTEROUS FAUNA OF PORTLAND. 



inland dark form have, from time to time, come on to Portland by 

 way of the Chesil Beach, and have, in conjunction with the white 

 thoroughbred Portlanders, caused all these intermediate forms that 

 we see. The dark variety is, as I said, rare in Portland, which 

 would be the case according to the above theory ; for, though the 

 moth may very well occur on the Chesil Beach, it is certainly not 

 abundant there, and, therefore, the coming of a specimen into 

 Portland would not be of frequent occurrence, and any but the 

 original immigrants would probably be more or less light in colour. 

 I have noticed that if one takes three or four mercurella close 

 together they are often all of about the same shade of colour. 

 Should further observation prove this to be generally the case, it 

 would tend to shew that the individuals of one brood did not vary 

 much among themselves, and hence that if no fresh specimens had 

 been imported, all the S. mercurella in Portland would resemble 

 each other far more than they do, and would probably be by this 

 time var. Portlandica, or something very near it. With regard to 

 the opposite case of a var. Portlandica finding its way to the 

 mainland, if such a thing did happen, it would there have no 

 advantage over the dark form, and its effects would probably be 

 scarcely visible after a few generations. 



Of other light forms, I think the most striking is the light form 

 of Grnoplws obscurata, which is found at Portland. This species 

 varies much in depth of colour and distinctness of markings, those 

 from the heaths in this county being very dark grey, whilst those 

 at Portland are much lighter, very light grey as a rule. This 

 species is found in many localities and varies much, but is generally 

 fairly constant in its shade in the same place. 



Larentia olivata and Epunda liclienea are rather light in colour 

 at Portland. On the other hand, Camptogramma bilineata is dark, 

 and Cnepliasia conspersana is much darker than on the Lulworth 

 and Swanage coast. 



I took a nearly black variety of Xylopliasla polyodon, and I 

 believe that Colonel Partridge took a similar one ; all other specimens 

 of this abundant moth that I have seen at Portland have been, 



