VAKIETIES OF NOCTU^ IN THE BRITISH ISLANDS. 353 



we have the first of those protean species where the ground 

 colour varies through several shades of colour, and where the 

 markings are so variable, and yet recurring with such frequency 

 in the various forms, that it is no wonder our early lepidopterists 

 thought they had many distinct species. Taking the first two 

 species, hasilinea and pahulah'icula, we have two of the most 

 constant species in the genus, basilinea being ordinarily charac- 

 terised by no special markings, but being generally of an almost 

 unicolorous hue with transverse lines, while pabulatricula is 

 characterised by a strongly-developed black longitudinal mark 

 directly under the stigmata. The two forms — represented by 

 these species — give a basis on which the development of the 

 variation in the other species appear to proceed, viz., (1) an 

 unicolorous form with transverse lines, and (2) a more variegated 

 form with a dark longitudinal streak under the stigmata. 

 The species of this genus may be looked upon as having the 

 anterior wings divided into three parts, — the basal area, the 

 median area, and the outer area. The first and last of these have 

 transverse lines crossing them, the second contains the stigmata, 

 and under this, in some species, is a very dark longitudinal 

 »-H - shaped mark (a modification of the claviform). These may 

 be looked upon as the great characters of the variable members 

 of the genus, the variation consisting principally of the develop- 

 ment (in some cases to a very high degree) or non-development 

 of this particular mark. Thus, in the variable species gemina, we 

 find all the different phases of variation to consist of two types : 

 one, in which the transverse lines are developed, and the species 

 has a particularly reticulated appearance ; the other, in which 

 the hH-shaped mark is highly developed, the transverse lines 

 more or less suppressed, and the median space more or less 

 intensified in its upper half in colour. But just as basilinea and 

 pabulati'icula exhibit single forms of a different type, and gemina, 

 on the other hand, exhibits these types blended into one with 

 intermediate forms, so we have in unanimis an almost purely 

 dimorphic species, where one form is reticulated and the other 

 with the >— (-shaped mark, and yet there is no extreme develop- 

 ment of either form, as in gemina. We now come to another 

 constant member of the group, — ophiogramma, — with its charac- 

 teristic dark costal mark, and then we reach, wliat appears to me, 

 to be the most aberrant* member of the group, leucostigma, where 

 the transverse lines are reduced to a minimum, where the 

 ►H mark is rarely developed, but where we get a perfectly new 

 form of variation, — a dark unicolorous form with no markings 

 whatever, except the variable yellow or white reniform stigma. 

 And then comes didyma {oculea), one of the most protean species 



* This is an Apamea, undoubtedly, from its markings, but the shape of the 

 wings is different to the other members of the group. It appears to have close 

 characters with Hydracia. 



