1890.] 



COLLECTED BY DR. EMIN PASHA. 



445 



5. Petbodkomus teteabactylus, Peters. 



a-c. Mandera. 3/90. Coll. by Lieut. Langheld. 



In this species it is worthy of note that there is a very considerable 

 difference in size between the sexes, a difference so groat as at first, 

 with only unsexed specimens for examination, to make one suspect 

 specific distinctness. Thus a male skull in the Museum collection 

 measures 50 millim. in basal length, whilst that of a fully adult 

 female is only 45. 



Specimen c has its milk-dentition still in place, and a figure of it 

 may be of use. Its interest, however, lies, not in the mere form of the 

 milk-teeth, but in their proving that all the usually received dental 



cOc= €£; 



**^ C3E>!^ 



Milk-dentition of Petrodromus tetradactylus. 

 Side and top view of upper and lower teeth. 



formulae of the members of the family are wrong in one important 

 essential. So far as I know, without exception, every author has 

 considered that the MacroscelicUdce have three premolars, and three 

 molars above and below, except Macroscelides brachyrhynchus and 

 M. fuscus, which have four molars below. This last fact might 

 have aroused a suspicion of what is really the case, as proved by the 

 milk-dentition, namely, that in all the members of the family there 

 are four premolars, the last three changing, as is usual, and only 

 two molars in the ordinary forms, the above-mentioned two species 

 having three below. 



This is rather a remarkable example of the many mistakes which 

 occur owing to naturalists homologizing teeth from their form alone, 

 for in this case, what is now proved to be P.^ is in its shape 

 absolutely molariform, so that it has hitherto always been taken to 

 be M.\ 



