Annals of the Transvaal Museum 67 
to juveniles throughout the order, viz. the presence of only three malleoli 
on the hind limb, was represented as characteristic of Hexisopus and 
was even included in the definition of the family Hexisopodidae. Other 
more important characters were of course mentioned in the original 
definition and all later writers have agreed in recognising the family. 
The best account of the genus is that given by Dr Purcell (9) who sums 
up the principal points of distinction from the Solpugidae as follows: 
the absence of one joint of the trochanters in each leg of the three pos- 
terior pairs : the absence of claws in leg IV : the extreme shortness of the 
distal portion of leg IV in proportion to the basal part : the length of the 
distal segment of the claws in legs II and III : the minuteness of the third 
tarsal segments in these legs : the absence of subungual appendages in 
these legs: the presence of a genital papilla in the male: the shortness of 
the upper lobe of the rostrum. 
Prof. Kraepelin in Das Tierreich also relies mainly on the characters 
of the legs in distinguishing this family from the Solpugidae: the great 
length of the segment now termed the trochantin and the shortness of 
the femur of the fourth leg is cited as an important character, and indeed 
the difference from the other known S. African genera in this respect is 
very striking. Other characters mentioned by Kraepelin in his diagnosis 
of the family, in addition to some of those emphasized by Dr Purcell, 
are: — mandibles with anastomosing stridulatory ridges: mandible of 
male almost toothless: ocular tubercle conical, forwardly projecting, and 
very hairy anteriorly: characters of the male flagellum. 
In my opinion none of these characters can be regarded as equivalent 
in importance to those which distinguish the two main families of 
Solifugae, viz. the Galeodidae and the Solpugidae. The great reduction 
in length of the distal segments of the legs, the strong development of 
spines on these segments and the disappearance of the tarsal claws of 
the fourth leg are doubtlessly to be regarded as adaptation characters, in 
accordance with the burrowing habit : such differences between Hexisopus 
and a typical Solpugid can be compared with those which exist between 
our short limbed, stout bodied, burrowing frogs ( Rana delalandi Tschudi) 
and the long limbed, slender, grass frogs ( Rana fasciata) of the same 
genus, and indeed are not very much greater than those which separate 
the sedentary females of the genus Stasimopus (trap-door spider) from 
the free-living adult male of the same species. The supposed reduction 
in number of the trochanter segments is incorrect, being based on an 
error of homology. The number of tarsal segments, the absence of sub- 
ungual appendages from the tarsi and the absence of claws on legs IV 
are characters of no great importance in view of the wide variation that 
is now known to occur on the several legs of true Solpugids. The short- 
ness of the upper lobe of the rostrum is apparently a feature peculiar to 
Hexisopus, and is not found in the closely related genus Chelypus. The 
stridulatory area of the chelicerae, which in Chelypus is not ribbed but 
marked with fine and quite irregular furrows,. seems to be much more like 
that of a normal Solpugid in some species of Hexisopus where parallel 
stridulating ribs are present : in any case, however, the character is not 
of great value seeing that in the same species of Solpuga ribs may be 
