96 
Transactions of the Uoyal Society of South Africa. 
has been well discussed by Dr. Purcell (15). The external structure of 
scorpions presents quite a large number of variable characters, but, as. 
Dr. Purcell emphasised, the majority of these, in the genus Opisthophthal- 
mus at any rate, cannot be used in the separation of species ; the variation of 
these characters is in short quite continuous. 
Characters which are to be regarded as essentially mutational seem to* 
be rare. The stridulatory lamellae on the chelicerae of many species of 
Opisthophthalmus must certainly be regarded as new characters which have 
arisen quite suddenly in the genus. In the typical form of 0. latimanus 
those lamellae seem to be constantly present : in all specimens I have been, 
able to examine of the form heilandsi they were constantly absent. They 
are absent in specimens of glahrifrons from certain localities, present in 
specimens from other localities. In a strict sense, however, this cannot be 
regarded as a unit character, for the number of lamellae when present 
varies considerably even in specimens from the same locality. Moreover^ 
I have seen an example of glahrifrons in which lamellae are present on one 
chelicera, but completely absent on the other chelicera. 
So far as I can ascertain, the external structure of scorpions in the 
genus Opisthophthalmus presents no character which behaves throughout 
the whole range of the genus as an absolute unit, which is either fully 
present or completely absent. If we consider any character whatsoever it 
will be found to present a gradational series of variations throughout the 
genus, though in particular species the character may be remarkably 
constant. A very constant character is the presence or absence of a well- 
developed Y-shaped fork on the frontal area of the carapace, but the 
partially developed fork which occurs in some species may fairly be re- 
garded as intermediate between the two conditions. ISTevertheless, although 
the conception of absolute unit characters cannot be strictly entertained for 
the whole genus, there is undoubtedly a real difference between the con- 
stancy of characters which distinguish allied species living together in the 
same environment and those which distinguish geographical varieties of 
the same species. In describing Opisthophthalmus peringueyi, Dr. Purcell 
stated that almost the only important difference between that species and 
pallidipes lies in the granulation of the carapace, the numerous very coarse 
granules on each side of the interocular area so characteristic of pallidipes^ 
being replaced by comparatively fine granules in peringueyi. Now this 
character is noteworthy in the genus for its relative constancy, and Dr. Purcell 
speaks of it as an excellent specific character. These two species, peringueyi 
and pallidipes, are both represented in our collection from Steinkopf . If we 
turn to a totally distinct group of the genus we find the two species macer 
and fossor separated principally by the same character and living in the same 
area (Caledon and Worcester Divs.) ; and the same applies to macer and 
chaperi, which, according to Dr. Purcell, occur in equal abundance on the 
