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Show 1 900.] MAMMALS FROM MOUNT KENYA. 179 The mammals obtained by Mr. Mackinders party at Nairobi are as follows:- 1. CERCOPITHECUS ALBIGULARIS Sykes. a, b. 2 • Nairobi Forest, 14/7/99. 2. FUNISCIURUS JACKSONI de Wint. a-e. 2 . Nairobi Forest, 5600 ft., 14-20/7/99. 3. MUS HILDEBRANDTI Petei'S. a. 2 • Nairobi, 6000 ft., 12/7/99. This Mouse is determined on the authority of Mr. de Winton, by whom the above name has been placed on Mr. Jackson's examples of it from Ravine Station. 4. ARVICANTHIS ABYSSINICUS Riipp. «. d . Nairobi, 16 July, 1899. This specimen appears to be conspecific with Uganda specimens of Arvicanthis determined by Mr. de Winton as A. abyssinicus. 5. TACHYORYCTES SPLENDENS IBEANUS, subsp. n. a. d . Nairobi Forest, 20 July, 1899. Similar in all essential respects to the typical Abyssinian form, but rather larger, and on the average rather darker in colour, especially on the head. For some years I have known that my reference of the East African Tachyoryctes to T. splendens was very doubtful, and have now taken the opportunity to investigate the question with such further material as has come in up to the present time. On laying out the Museum series of skulls, 9 from East Africa and 5 from Abyssinia (including one of Riippell's co-types), it is at once evident that the former is a larger and more powerful animal, but is in other respects very closely allied. Even as to its greater size, although there is no doubt of the fact, there is some difficulty in reducing it to measurement owing to the way these animals go on increasing in size until a late period of life, so that old specimens of the small form may overtop in most measurements the nearly adult specimen of the larger. But taking only old specimens, two of each form, with sagittal crests completely developed, the following comparative measurements may be given :- Basilar length. Greatest breadth. Diastema. T. s. typkus . . . . 37-5, 37-2 28, 30-5 167, 16-2 T. s. ibeanus 43, 4P5 34, 325 18-3, 19 In all adult skulls also a diagonal measurement across the brain-case from the squamosal edge above the meatus of one side to the most bulging antero-lateral corner of the brain-case on the other will illustrate the difference between the two forms, this |