528 MR. L. DONCASTER ON COLOUR-VARIATION [ Dec. 12, 
5. On the Colour-Variation of the Beetle Gonioctena 
variabilis, By L. Doncastsr, M.A., F.Z.8. 
[ Received July 7, 1905. } 
In 1895 (P. Z.S. 1895, p. 850) an account was given by Mr. Bate- 
son of the colour-variation of Gonioctena variabilis, a Chrysomelid 
beetle. His material was collected almost entirely at Granada 
in the months of March and April; and he found that although 
the insect is extraordinarily variable, yet when a large collection 
is made the beetles could be classified into two chief groups with 
very few intermediates between them. The ground-colour of 
the elytra varies from a brilliant red through orange and buff to 
a greyish green; and although the intermediate colours (orange 
and buff) are comparatively rare, no sharp line between the red 
and green can be drawn. There is also a great diversity in the 
markings: some individuals, chiefly those with red elytra, have 
two black spots on each elytron (spotted type), others (almost 
exclusively greens) are without these spots but have rows of 
minute black dots (striped form), and a third class has both spots 
and stripes. A large series of figures is given in the paper 
referred to. Bateson further found that the spots and stripes 
have a definite relation to the sculpturing of the elytra; the 
spots having their centres on certain of the longitudinal rows of 
punctulations, while the stripes lie between them. The spotted 
or striped type may be associated with either the red or green 
colour, but Bateson observed that almost invariably the spotted 
elytra were associated with black pigmentation of the ventral 
surface of the abdomen, and that specimens with no spots had 
no black pigment in this position. The colour of the underside 
therefore provided a means of dividing a population into two 
classes with exceedingly few intermediates; some had dark 
undersides and spotted elytra (with or without stripes in addition), 
the remainder had light undersides and were without spots. 
When classified in this way, it is found that most of the dark- 
spotted specimens have red or reddish elytra, and most of the 
unspotted light are green; and further, that about 80 per cent. 
of the first class are males, and about 70 per cent. of the second 
class females. The males are easily distinguished from the 
females by the presence of a small rounded depression in the last 
uncovered abdominal plate; this is absent in the female. 
In addition to the variations mentioned, there may be more 
or less suffusion of the elytra with black pigment, until a totally 
black form is reached. The specimens in which this melanic 
variation is not very pronounced show that they belong to the 
class which is both spotted and striped; it occurs much more 
frequently in red than in green individuals. 
