| OCR Text |
Show 1890.] COLLECTED BY DR. EMIN PASHA. 445 5. PETRODROMUS TETRADACTYLTJS, 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 great 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 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 Macroscelididce have three premolars, and three molars above and below, except Macroscelides brachyrhynchits 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 iu 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 n o w proved to be P.4 is in its shape absolutely molariform, so that it has hitherto always been taken to be M.1. |
