14 
Annals of the Transvaal Museum 
genus, the characters which distinguish the several forms commonly 
termed species are not of an essentially discontinuous type. There is a 
small group of species, characterised by the more or less strongly twisted 
shaft of the flagellum, and the presence of serrated edges along some 
portion of this shaft. These species ( spiralicornis , serraticornis and 
strepsiceros ) seem to represent separate links in a chain of continuously 
varying forms: a complete series of intermediate forms is not yet known, 
but sufficient variation has been noted in a small series of spiralicornis, 
and in several specimens of serraticornis, to indicate that the specific 
distinctions, though greater in magnitude, are essentially of the same 
kind as those which are now included within the limits of the same 
species, and which are clearly of the continuous type. I suspect it will 
eventually be found that the species cervina, collinita and alcicornis are 
also forms of one continuous series : and apparently another such series 
is that of lethalis typicus, lethalis rectus and furcifera. 
Amongst the nocturnal species, which constitute the most primitive 
group of the genus, it sometimes happens that the only noticeable 
differences between species are those of the flagellum. This is the case 
with S. lethalis and S. Venator, for the minor difference of dentition which 
is also said to distinguish them is not constant, and moreover is com- 
monly found within the limits of a single species. 
In these nocturnal species, the dentition of the male greatly resembles 
that of the female, and several other characters of the chelicerae, viz. 
the strong development of stridulatorv ridges, and the abundance of 
well-feathered bristles in both upper and lower jaws are common to both 
sexes. 
More usually, profound differences of dentition, or of spinulation, 
accompany the variations of the flagellum. Sometimes indeed, the 
characters of the flagellum may remain very constant throughout a 
group of forms which differ amongst themselves in the dental characters. 
This is the case, at least so far as the shaft of the flagellum is concerned, 
throughout the species hostilis, derbiana, and tookei, the most character- 
istic feature of the shaft being its sharp blade-like termination : this same 
blade with modifications also occurs in hamata and bechuanica : it seems 
to be quite constant in hostilis, but is variable in derbiana, and therefore 
cannot be regarded as an absolute unit character in a strict sense. 
The variations of dentition in the hostilis group of species are indeed 
very numerous. The dentition is comparatively constant within the 
limits of any one form, and such forms as hostilis may have a fairly wide 
geographical range : but, we are still uncertain whether the various types 
are fundamentally distinct, or are units of one or several continuous 
series. The occurrence of a dentition so aberrant as that of junodi in the 
midst of an area occupied by allies ( hostilis , marshalli) which share the 
most characteristic feature of quite a different dental type, is suggestive 
of mutational variation. On the other hand, the additional material 
received during recent years has to some extent served to bridge the 
wide gaps which formerly seemed to separate types so distinct as 
chelicornis, hostilis and junodi. The typical form of chelicornis, found in 
the karroid portions of the Cape, is represented at Kakamas by a dis- 
