Annals of the Transvaal Museum 
91 
186. Myztromys albicaudatus fumosus, Thos. and Schw. 
1 $, 2 yg. <J, 2 juv., Wakkerstroom (3 Roberts, 2 Jameson). 
? 1, Modderfontein, Transvaal (P. J. Pohl) (skull in skin). 
187. Mystroinys albipes , Wagn. 
2 $, Wonderfontein (Jameson). 
188. Petromys typicus , A. Sm. 
1, Klipfontein (Grant). 
189. Ileliophobius argenteo-cinereus , Ptrs. 
8, Boror (Kirby and Roberts). 
It is not quite clear from a study of these specimens that two species 
do not occur side by side, but as the differences which can be observed 
are confined to the two sexes, it is possible that this species is dimorphous. 
An adult male with five back teeth has a white blaze on the forehead, 
long nasals produced backwards level with or slightly beyond the fronto- 
premaxillary suture, and with the outer lateral nasal sutures straight. A 
smaller <J, with the hindmost molar only just appearing, has a smaller 
white blaze and the nasals are like those of the larger specimen. Four 
large and one small $ have four or five back teeth, which show some 
remarkable anomalies in their rate of growth and number on either side 
and jaws ; in them the nasals are shorter, bulge out laterally towards the 
back, and then narrow off either to a point or a semicircle, while the sides 
of the premaxilla are produced backwards behind them, thus forming a 
forward projection of the frontals where they meet the nasals. In a very 
much smaller specimen the nasals are similar to those of the $$ ; it has 
the rudiment of a milk tooth on one side of the lower jaw, three back 
teeth of the normal size and the fourth just beginning to show ; it is too 
young to be of use in settling the question of whether two species occur 
side by side or whether all the specimens are referable to one species. 
The teeth present so many anomalies in the series, that a brief discussion 
may not be out of place. 
The hindmost molar appears to grow out in two divisions, the 
posterior half of which is often only half the length of the anterior when 
it has grown to the level of the adjoining molar. The first premolar is 
not always present, or may be present on one side only. The second 
premolar (if it be a premolar) is small and of the same size throughout 
the series, including the very young male ; and the remaining molars are 
apparently equivalent to those of Georychus. The roots of the molars in 
the upper jaw curve strongly outwards, and in the lower jaw are either 
straight or curved slightly inwards. The rate of growth of the hindmost 
molar is, more often than not, much faster on one side than on the other, 
so that though the one may present a worn appearance that on the 
opposite side may not yet have reached the level of M\ 
The following is a table of measurements given in four divisions : — 
<$($• Largest Smallest Youngest 
H. and B. 
151 -182 
165 -179 
145 
— 
Tail 
12 
8-14 
13 
— 
Hd. ft 
Skull : — 
31 - 33 
28 - 31 
28 
— 
1-cond. lg. ... 
46 - 47*8 
40-5- 41*5 
40 
34-6 
Nas. cond. leng. 
41 - 43*3 
36*3— 36*6 
36*4 
30-7 
Zyg.br. 
30*3- 32*4 
27*3- 29-2 
27-3 
25 
Br. case 
17*3- 18-4 
16*1- 17-2 
15*8 
15-5 
Nas. leng. 
14-4- 15*1 
11*2- 12-8 
13 
10*1 
Nas. br. 
4-7- 4-9 
4*2- 4-9 
4-2 
3*7 
