270 Dr. Frederick A. Dixey on the 
there exist a true discoidal spot. The nearest approach 
is to be found in G. napi, where the disco-cellulars of the 
forewing, together with the other nervules, are in many 
specimens accompanied by a sprinkling of black scales ; 
which in some instances are sufficiently numerous in this 
particular region to give almost the appearance of a 
black discoidal spot or patch. This may be best seen in 
specimens of G. bryonix, but dusky specimens of the 
ordinary G. napi will sometimes show the tendency 
almost equally well. The same tendency is carried a 
hittle further in Tatochila autodice, while JT’. theodice 
shows the corresponding marks in a condition of strong 
development, with a slight indication of a similar feature 
on the hindwing as well. Passing to the genus Synchloe, 
we find the discoidal spot invariably present, at least in 
the forewing; and in most species large and distinct, 
especially in the females. SS. daplidice (Fig. 15) has the 
spot well developed on both surfaces; on the lower sur- 
face it is more or less shaded with green. The same is 
the case with the somewhat smaller discoidal spot in 
S. callidice. Another example of a large and conspicuous 
discoidal spot is furnished by S. hellica. 
In Colias, a discoidal spot is nearly always present on 
each surface of both fore and hindwings. On the upper 
surface of the latter it is sometimes independently 
present and sometimes only shows through from 
beneath ; but it is seldom absent altogether. The spot 
on the forewing is in this genus, as in Synchloe, usually 
dark brown or black. It may be ringed or pupilled with 
orange; in the former case the orange is of a deeper 
shade than the general ground-colour. Hxamples of 
this may be seen in C. meadit, C. cunninghamii, and 
others. In C. fieldii and C. edusina the discoidal spot in 
the forewing is unusually large; in no species of Colias, 
however, does it overpass the boundaries of the sub- 
costal nervure in front and the third median nervule 
behind. It may be very small, as in C. barbara; or 
entirely absent, as in some specimens of OC. paleno and 
C. pelidne. On the lower surface it is often centred with 
white or silver. On the upper surface of the hindwing, 
the spot when present is not dark, but varies in different 
species from the palest yellow to a full orange. It is 
distinguished from the general surface of the wing either 
by its different shade of yellow or orange (as in C. hyale) 
