Georyclius and its Allies. 443 



pliape, and old ones o£ the latter, but individual exceptions to 

 this rule are very numerous. No doubt the shape of the 

 foramen is a good enough character, if care be taken tliat it 

 is regarded as an average and not an invariable one, but 

 species should certainly not be described on it alone witliout 

 quite considerable series. 



Of course, in species isolated geographically, such as Cryp- 

 tomys foxi or zechi, the characters are more constant, but 

 where, as in the soutliern half of Africa, the animals are 

 found everywhere and no barrier to distribution exists, it 

 may almost be said that any character of skull may be found 

 in any species, thus absolutely nullifying geographical splitting 

 of tlie usual type. 



Even size, when the giant northern species are put aside, 

 is of but little use, for in any series of skulls a few individuals 

 will be found much larger than the great majority, these 

 animals appearing to add to the bulk of their skulls long after 

 they have attained adult life. For example, the type-skulls 

 of both C. hoeagei, de Wint., and C. ivhi/tei, Thos., are so 

 much larger than others from the same areas that they might 

 readily be thought specifically different from them. 



Of course, I do not mean that the skull-characters are 

 negligible, but only that a much more liberal view of their 

 inconstancy and want of importance should be taken than is 

 the case in other mammals. Let anyone look at Mr. Austin 

 Roberts's figures of skulls, and he will see how essentially 

 similar they all are to one another. 



The mammary formula of Cryptomys appears to be always 

 2 — 1 = 6. At least, this is the number 1 find in every spirit- 

 female we have, whatever its locality. Mr. Roberts's state- 

 ment that some of the species have no inguinal pair is probably 

 due to his having attempted to count mammre on fresh speci- 

 mens, which is almost as difficult and untrustworthy as doing 

 so on skins. Spirit-specimens are alone to be trusted for 

 this particular purpose, as every mammalogist of any expe- 

 rience is aware. 



It may be of interest to record that Cryptomys — or, at 

 least, some of the species of it — possesses that most unusual 

 structure, an os clitoridis. In a specimen of G. mechoioi it is 

 an oblong flattened bone 5 mm. in length, I'S in breadth, and 

 0"5 in thickness, not very much smaller than the corresponding 



both from the same farm at Willbrook, Estcourt ( Wroughton ^- Turner), 

 which equally have the extremes as regards the posterior nasal reo-ions 

 other specimens from the same series filling up the gap between them. 



