JOURNAL OF VARIATION. 
No 
VOL. II. 
May 15th, 1891. 
THE GENUS ACRONYCTA AND ITS ALLIES. 
By Dr. T. A. CHAPMAN, F.E.S. 
{Continued from page 2.) 
\CRONYCTA {Cuspidia) tridens. — We begin here that 
section of the genus in which the eggs are laid 
solitarily, the moth in the wild state probably taking 
a flight after the deposition of each egg. The egg 
(PI. VIII., fig. 2) of tridens is nearly colourless, almost glassy 
when first laid, but acquiring a certain whitish opalescence as 
the young larva within is developed. Its greater size, and, to a 
slight degree, the ribbing, render it only slightly less favourable 
for the observation of the embryonic development than those 
of Botys hyalinalis, for the opportunity of observing which 
species I am indebted to Mr. Jeffrey, of Ashford. The egg 
being solitary takes the very regular form of a portion of a 
sphere, less than a hemisphere, or roughly, that of a bun. The 
diameter is *83 mm., and height *38 mm. The ribs are 38 in 
number ; in all the Acj'onyctas this number varies, and the 
numbers I give are either the average or the actual number of 
a particular specimen counted. The egg of tridens rarely, if 
ever, exceeds 44 ribs, that of psi as rarely has less than 45. 
In colour, or rather want of colour, secondary ribbing, form, 
etc., they seem to be identical. When about to hatch, the 
young larva is very conspicuous inside, the head forming a 
central black spot. 
The newly hatched larva (PL VI., fig. 2) is paler than it 
shortly becomes, but the head is already black, and the pale 
and dark segments are clearly pronounced. Each tubercle is 
a large flat plate, somewhat angulated, so as to fit against 
and amongst the others ; this feature is common to a number of 
Acronyctas. The trapezoidals are thus somewhat pear-shaped, 
the anterior with the narrow end backwards, the posterior with 
