100 'Apil. 



down to very dark warm brown ; in both there is often a strongly ochrcous tinge, 

 but in the darker forms of the latter the colour is generally brown or ochreoiis-lrown, 

 as opposed to the grey or ochreous-grey of the former. The variation in colour is 

 shown in both sexes. 



2. The basal area (exclusive of the extreme base, which is in both species often 

 of a different colour) in eratceyella is either of the same shade as, or inost frequently 

 darker than, the medial area, whereas in its ally the basal area is almost invariably, 

 to a greater or less extent, rather the lighter of the two. 



3. In cratcBgella the medial area is never conspicuously darJcer than the rest of 

 the wing, as is often so noticeably the case in mercureUa, owing to the presence of a 

 darker cloud along the outer edge of the first line and towards the costa. In dark 

 examples of the former, there are sometimes indications of this dark clouding, but, 

 even then, owing to the still deeper shade of the rest of the wing, its presence does 

 not render the medial area conspicuously dark. 



4. Owing to the usual absence of this cloiuling in crattegella, the orbicular and 

 claviform stigmata are, as a rule, much more distin-ot than in the allied species, in 

 which they are fi-equently much obscured. In cratagella the claviform stigma 

 often takes the shape of a black dot placed at a little distance from the first line, 

 extremely rarely, if ever, touching it ; but in mercureUa it is usually dash-shaped, 

 and touches the first line. 



No reliance, however, can be placed on these two stigmata ns a permanent basis 

 of tabulation for the genus, as is done by Dr. Guard Ivnaggs in the Ent. Mo. Mag., 

 V, p. 291. In both the species under consideration they undoubtedly vary to a certain 

 extent in shape, and consequently in relative position as regards the first line. 



5. Cratagella has the 8 mark small, and outlined by a narrow and clearly- 

 defined dark line ; the upper half is generally filled in with the palest shade of the 

 ground colour, and stands out clearly as a neat, round, eye-like spot. In mercureUa, 

 however, the 8 mark is, as a rule, larger, and situated nearer the second line ; it is 

 by no means so clearly outlined, and the upper half is usually filled in with a darker 

 shade than the ground-colour. It consequently never presents to the same degree 

 the neat and striking eye-like appearance. 



6. In cratagella the second line is very dark and clearly defined, both on its 

 outer and inner edge ; it is distinctly marked right across the wing from the 

 costa to the inner margin. In mercureUa, on the other hand, there is sometimes in 

 the darker forms no real second line, but simply an abrupt termination of the dark 

 medial area ; when a genuine line appears, it is not relatively so dark or so clearly 

 defined, particularly on its inner edge, and, while strongest on the costa, is apt to 

 fade away, or become much less distinct towards the inner margin. 



7. In both species the second line is followed by a distinctly pale line, but in 

 cratagella this is always decidedly narrower tlian in mercureUa, and is never rela- 

 tively so pale in comparison with the general shade of the wing ; in the latter it 

 often forms, more properly speaking, a band, which reaches its extreme breadth in 

 the whitest yaw, portlandica. 



8. The distinction, noticed by Mr. Stainton in the " Manual," ii, p. 162, that in 

 cratagella the upper half of the sub-terminal band unites with the dark wedge- 

 shaped mark on the hind-margin, whilst in mercureUa it is not so united, holds good 

 in the great majority of cases, though it cannot be altogether relied upon. 



