129 MULIYIL NARAYANAN. 
culum into two separate plates has not in itself any generic or 
specific value, but is, in many cases at any rate, a sexual char- 
acter only. 
In all the species of Scorpio, Androctonus, and Euscor- 
pius, which I have examined, the genital operculum consists 
of a single plate in the female; but in the male this plate is 
divided into two lateral halves. The genital operculum of the 
female, seen when the animal is viewed from the ventral 
aspect, is shown in Pl. IX, fig. 3 (VII. G.o.). It is a chitinous 
plate attached to the sternal region of the body immediately 
posterior to the so-called “ Sternum’”’ (the fused sternites of 
the fifth and sixth somites). Its posterior edge is unattached 
and free, so that it may be turned forward (PJ. IX, fig. 4). 
When thus turned forward the median oviducal aperture is 
visible. The operculum presents, on its sternal surface, an 
indistinctly marked longitudinal groove, and its margin at 
either extremity of this groove is clearly bifid. 
In the male a very different arrangement obtains. The 
genital operculum consists of two totally distinct pieces lying 
on either side of the median line; these may be called the 
opercular plates. When in its natural position (Pl. IX, fig. 
1) this is not very obvious, and except for a very slight 
difference in shape it appears to be like that of the female, 
the median groove being, however, more deeply marked. But 
if we attempt to turn it forward the groove is seen not to be 
a groove at all but an actual division of the plate into two 
lateral pieces. Each piece is hinged anteriorly, so that it can 
be turned forwards and outwards (Pl. IX, fig. 2). When the 
pieces are thus turned forwards the genital aperture is not 
visible as it would be in the female. It is hidden by various 
structures to be described below. 
A pair of processes which have hitherto, so far as I am 
aware, entirely escaped observation, is seen (Pl. IX, fig. 2, p7.). 
They are turned forwards and are triangular in shape, and are 
covered with light-coloured chitin, and doubtless serve as copu- 
latory processes. I propose to term these the “ sub-opercular 
plates.” The genital aperture is hidden by a transverse muscle 
