442 Mr. O. Thomas—WNotes on 
—the genotype—from the great mass of the species usually 
assigned to that genus, and proposed to recognize the two 
groups so distinguished as subgenera, accepting for the 
second subgenus the name Cryptomys from Dr. Gray’s paper 
of 1864 *. 
This division appears to me thoroughly sound, especially 
as, in addition to the tooth-characters mentioned by de Winton, 
there is a material difference in the structure of the posterior 
palate, Cryptomys having this quite normal, while in Geo- 
rychus (s. 8.) the capsules of the incisor-roots are extended 
backwards into the pterygoids in a mauner approaching that 
found in Heliophobius. 
On the whole, therefore, it would appear to be advisable to 
recognize Cryptomys as a full genus distinct from Georychus, 
the great majority of the described species falling into it. On 
the other hand, Gray’s Cetomys is not worthy of any sort of 
recognition. 
Restricted Georychus—the capensis group—inhabits the 
extreme south of Africa, ranging northwards to Namaqualand 
on the west and the Transvaal in the east. Cryptomys only 
overlaps it along a comparatively narrow zone, but ranges 
northwards from Knysna and Natal over the whole of the 
Ethiopian region to Nigeria and Togoland. 
As regards species, the genus Cryptomys is extraordinarily 
uniform both externally and cranially, the many forms 
described only differing, apart from size and a limited 
range in colour, by characters of but little importance, such 
as slight differences in the shape of the nasals, the relative 
lengths of premaxillary processes and the nasals, and the 
shape of the anteorbital foramina. Moreover, these diffe- 
rences, such as they are, are curiously inconstant in the 
group, almost any good series from one locality being liable 
to contain individuals with the characters supposed to be 
peculiar to other species. This is notably the case with the 
apparently important character of the anteorbital foramina, 
which in some cases may be high and lunate, with slender 
boundaries, or small and subcircular, with thick ones, in 
specimens taken in the same localities and obviously of the 
same species t. Young specimens tend to be of the former 
* P, Z.S. 1864, p. 128. 
+ The type-skull of G. nimrodi, de Wint., has a subcircular foramen 
on one side and a high one on the other, And anyone to whom the 
British Museum collection is accessible should compare 4. 3. 1. 88 and 92, 
both from Vredefort Road (Barrett-Hamilton), which have the extremes 
of difference in the anteorbital foramina, and 5. 5, 1. 14 with 14. 5. 4. 20, 
