276 Dr. Frederick A. Dixey on the 
In Terias and Sphzxnogona, D is constantly absent 
from the upper surface, but is usually visible below, 
where it may appear as a small black dot or pair of dots 
in each wing (7. lisa), or as a group of more or less 
regular narrow-bordered rings (7. hecabe and T. floricola), 
or in various intermediate forms (7. deva and S. gratiosa). 
The transition from the condition of D in Colias to that 
in Terias is well indicated by Xanthidia nicippe, most 
specimens of which correspond pretty closely in the 
markings of the lower surface with the latter genus ; 
while the upper surface of the forewing bears a discoidal 
spot much like that im some species of Colias. In the 
closely allied genus Pyrisitia, D has altogether disap- 
peared (see P. proterpia). 
The genus Huchloe shows the discoidal spot on the 
forewing in a well-marked condition (Fig. 24). It may 
exist as a distinct spot, as in H. cardamines, usually 
larger in the female; or as a more or less quadrangular 
patch reaching up to the costa, asin ZH. lucilla. On the 
underside it is often white-centred, as in H. belemia and 
others. On the hindwing, D is in many species of Huchloe 
not visible at all. In some, however, it appears as a 
small, at times very minute, patch of black scales sur- 
rounding the second disco-cellular nervule (some speci- 
mens of H. genutia and H. cardamines) ; in others, as 
E. charlonia and E. lucilla, it takes the form, on the 
under surface, of a pale circular patch, closely resembling 
D4 of Colias paleno in the same situation. 
D in Belenois is usually well marked on the forewing, 
as a rule enclosing both disco-cellulars, and often 
prolonged anteriorly to join the outer extremity of a dark 
costal band ; this is especially the case in the female, and 
on the under surface in the male, as in B. mesentina, B. 
teutonia, B. calypso, etc. The spot is sometimes small 
and quite distinct, as in B. creona, D 1 being absent ; 
sometimes, on the other hand, it is large and almost or 
quite merged in the general dark field of the outer 
portion of the wing, as in B.coronea. In the hindwing 
there may be no discoidal mark at all, as in B. creona; 
or all the nervures may be covered with dark scales 
(as generally on the under surface of B. mesentina), 
the disco-cellular nervules not being specially dis- 
tinguished; or there may be a definite discoidal spot, 
composed of D 4, as in B. mesentina ¢, upper surface; 
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