342 The Scottish Naturalist. 



Larentia didymata. — In Shetland and the Outer Hebrides 

 darker than usual ; in Orkney lighter than usual. 



Emmelesia albulata in Shetland departs very much from 

 the ordinary form, the colour being "luteous lead-colour" and 

 the markings more or less obliterated. The name var. Thules 

 has been proposed for this form. In Orkney the colour is 

 normal, but in the Outer Hebrides there occurred along with 

 ordinarily coloured specimens several pure white specimens, to 

 which the name var. Hebridium has been given. 



Eupithecia venosata. — Normal in Orkney, but in Shetland ot a 

 dull lead-colour, with the markings often ill defined. 



Melanippe montanata. — Normal in Orkney. In Shetland pre- 

 sents a well-defined variety (Shetlandica) in which the median 

 band is much broken up and the hind wings streaked with 

 narrow dark lines, the ground-colour being pale or dark. In the 

 Outer Hebrides the specimens are small and the ground-colour 

 suffused with grey, but the median band is not broken up. 



Camptogramma bilineata. — In Shetland this is of a pale straw 

 colour, but, as usual, the markings vary in intensity. In the 

 Outer Hebrides there is a grey look about the front wings. 



Cidaria russata. — Very variable in Orkney. On the other 

 hand, in the Outer Hebrides there is a striking uniformity in the 

 coloration — the more remarkable as this insect is usually so 

 variable — grey and black being the prevailing colours, and the 

 usual red markings being very faintly shown. The size also is 

 smaller than usual. 



Though the above are the more striking variations afforded 

 by individual species, yet if collections from each of the three 

 groups of islands are examined, they present, when compared 

 inter se, certain noteworthy features. The Orkney insects differ 

 very little, if at all, from those of the north of Scotland in general 

 appearance, nor, considering the proximity of Orkney to Scot- 

 land, ought we to expect this to be otherwise. The Outer Heb- 

 ridean insects are more differentiated than the Orcadian, and 

 amongst them, especially in the Geometras, the prevailing colour 

 is grey. In the Shetlandic insects the most striking feature is 

 not only a wider range of variation in colour, but that some of 

 the species have diverged into very well denned varieties. 



The special features of the insects of each group is just what 

 we might reasonably expect. Of the three groups the Orkneys 

 are not only the one most recently insulated, but from their 

 proximity to the coast of Scotland it is almost certain that in- 



