62 MR. O. THOMAS ON THE [Jail. 3, 



developed, and looking quite as if that species always possessed them. 

 Again, a specimen of //. (/racilis 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 

 H. albicauda and //. ichneumon, in the first of which the last molar 

 is from 7 1 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 Irom the imizzle to the upper lip. 

 I. Toes 5—5. 



a. Premolars j (if only o in either jaw, a cliasteiua 



always present) I. Herpestes. 



b. Premolars ff (no diastema in front of 1st premo- 



lar). Hind soles naked II. HelogAle. 



II. Toes 4— 4. 



c. Premolars -J. Hind soles hairy III. BDEOCiALL'. 



III. Toes 5— 4. 



d. Premolars j. Hind soles haii'y IV. vsictis. 



