4 
Annals of the Tbansvaal Museum. 
Pleurelra alpiurn (Ehr.) — The type did not occur, but the small dull- 
coloured form which was noted in tropical Africa (27), and is known also 
in Australia and Hawaii. 
Pleuretra africana, sp. n. (Plate I, figs. 2a-2e). — Specific characters : 
Large, brown ; neck with two very large conical processes, on either side 
of the a’ tenna ; some minute spines on the anterior margin of the trunk ; 
a dorsal series of ten warts crossing the central segments near the widest 
part ; in front of these two lateral warts at each side ; four spines on each 
of the two segments of what appears to be the rump ; foot four-jointed ; 
spurs very short and obtuse, separated by a wide interspace. Teeth two. 
General description . — Length about 400^. The antenna is long and 
stout. The conical processes on the neck are about 20^ in length. Though 
not in themselves mobile, they can be brought together as the animal 
contracts till they touch at the tips. The anterior margin of the trunk 
bears only a few tooth-like processes. The large furca which admits the 
antenna in most forms of P. hrycei is reduced to very small dimensions, 
and would not hold the antenna. The ventro-lateral spines on the anterior 
margin are absent. The main dorsal row of ten knobs is as in nearly all 
forms of P. hrycei, and the two lateral warts in front of the main row are 
common to many forms of that species. 
Ihe central trunk is nearly quadrate. Following it come two seg- 
ments which appear to form the rump, but there is some reason to think 
that the first of these is really homologous with the fourth central of most 
Bdelloids, and that the second, which appears to be the anal, really consists 
of the anal and preanal, very much shortened. Each of the apparent 
segments of the rump bears four warts. The foot is relativelv slender, 
the first joint long and bearing a small transverse dorsal ridge ; the second 
joint very short ; the spurs small. 
The skin is stippled and wrinkled like that of P. hrycei ; even the 
spurs are dotted. 
There is a very extensive series of forms, more or less closely resembling 
P. hrycei Weber (38), and they are so linked together that it is very 
doubtful if any of them can be separated as distinct species, though each 
form appears to be fairly constant in the locality where it occurs. I believe 
they are genuine races, which may be regarded as species or not, according 
to the conception of species entertained. 
Among all these forms which are known to me there is none which 
offers so many peculiarities as this one which I name P. africana, and 1 
have judged it more useful to regard it as a distinct species than as a 
variety. 
Whilst it is on the whole the best armed with spines of all the group, 
this is combined with the reduction or absence of some of the usual spines. 
Most of the forms have small rounded processes on the neck ; in this they 
are developed into great thick cones, which give the animal a very unusual 
appearance in some positions. 
The processes on the anterior margin of the trunk are greatly reduced, 
especially those nearest the dorsal middle line, which usually form a large 
furca for the antenna, and are themselves often furcate. There are none 
