--by the
difference in the ground tint of the wings, which in this vary from
primrose or sulphur yellow to a greenish white.

There is, however, some risk of confounding this with the white variety of
_Edusa_ (_Helice_), a mistake often committed by young entomologists; so it
will be well to point out the most prominent distinction between the two;
and this is easily done, by observing that in _Edusa_ the dark border of
the upper wings is of nearly {76} equal breadth along the whole of the
outer margin, and _at the lower corner is continued inwards for a short
distance_; whilst in _Hyale_ this border _narrows rapidly, and disappears
before reaching the lower corner of_ the wing. Also the dark border of the
hind wings is much broader in _Edusa_ than in _Hyale_. Here we have
distinctive marks, quite independent of the ground colour of the wings.

The sexes of this butterfly are nearly alike in their markings, the chief
difference being in the yellower ground tint of the males.

The same localities--viz. the south and south-east coast, and the adjacent
district--that are most prolific in its near relative, _Edusa_, likewise
furnish this species in the greatest plenty; but this is by far the rarer
species of the two, and, either by coincidence, or in obedience to some
direct law, several successive periods of its abundance have been
septennial, or have occurred once in seven years. Thus the years 1821, '28,
'35, '42, '49, and '56 are noted in entomological records as having
produced it in great numbers.

On the coast of France, opposite to our own, it is one of the common
butterflies, and it is not improbable that it frequently makes the passage
of the Channel. The maritime habits of both this and _Edusa_ are well
known, and I have frequently seen the latter flying out to seawards, and
coquetting with the waves, till the eye could follow the golden speck no
longer. Taking advantage then of a favouring wind, its naturally strong
{77} and rapid flight would quickly take it across the few miles of sea
that separate us from the Gallic shore.

_Hyale_, whose flight is at least as strong as _Edusa's_, and whose
salt-water tastes are similar, doubtless acts in the same manner.

The northward range of this species is more limited than that of _Edusa_,
but it has been taken singly near York, Manchester, and a few other
northern localities. In the lucerne fields near Brighton, a dozen or more
have been sometimes captured in one