62 MR. 0. THOMAS ON THE [Jan. 3, 
developed, and looking quite as if that species always possessed them. 
Again, a specimen of H. gracilis has an additional lower premolar 
standing side by side with the third normal one ; but this differs from 
the last instance in being more obviously an abnormality. The type 
of Rhinogale melleri, as mentioned below (p. 81), has one more 
upper premolar on each side than is found in any other species of the 
group; but as, so far as I know, this typical specimen is unique, I 
cannot say whether the dental formula possessed by it is constant or 
not. On the other hand, a deficiency in the full number of teeth is 
very common, all the species with normally four upper premolars 
often losing the first one, which when present is always much 
smaller than any of the others. 
It has just been mentioned that the dimensions of the teeth are 
very constant ; and so much is this the case that I have found that the 
comparative measurements of the fourth upper premolar and second 
molar afford very good specific characters; for in those species in 
which the teeth are more or less round and suitable for grinding 
rather ‘than cutting, the second molar is of considerable size and the 
fourth premolar is but little larger, while, on the other hand, when 
the teeth are slender, angular, and with cutting-edges, as in H. ichneu- 
mon, the last molar is very small and rudimentary and the last pre- 
molar is large and has a well-developed anterior internal process. 
As an instance of these differences, I may mention the cases of 
Hi. albicauda and HH. ichneumon, in the first of which the last molar 
is from 71 to 84 per cent. of the fourth premolar, while in the latter 
these percentages range only from 42 to 45. 
The measurements upon which these percentages are founded are 
those of the greatest diameter of the tooth—in the fourth premolar 
from the posterior point of the tooth to the anterior edge of the 
internal lobe, and in the last molar simply the greatest transverse 
diameter of the tooth. The percentages obtained by these measure- 
ments are called in the synopses of the species the ‘dental per- 
centages ;’’ and a table is given at the end of each genus showing the 
exact dimensions, with the resulting percentages, of the teeth of its 
members. 
Synopsis of the Genera. 
A, With a naked groove from the muzzle to the upper lip. 
I, Toes 5—5 
a. Premolars + (if only 3 in either jaw, a diastema 
ALWAYS PLesenb) Binwernsterctteptaveasinaerase sesere sees J. Hurresres. 
2, Premolars 3 (no diastema in front of Ist premo- 
lar). Hind solesmaked ....0tii..s..cer0-00 ses teedes II. Henocare. 
II: Toes 44. 
c. Premolars {- Hind soles hairy .i....c:ciccceseceee III. Borocsne, 
III. Toes 5—4, 
d. Premolars {. Hind soles hairy ...scsssccsessesesees IV. Oyyiciis. 
