92 On the Psammomys of the Nile Delta. 



the borders of the western desert. We owe to the late 

 Dr. J. Anderson topotypical examples of this form. 



Now Mr. M. J. Nicoll, of the Giza Zoological Gardens, has 

 sent a series of Psammomys from Damietta, on the dark 

 alluvial soil, and these, while agreeing in other respects with 

 the Alexandrian species, are so uniformly darker that they 

 should evidently be recognized as a local subspecies, to which 

 I would assign the name 



Psammomys ohesus nicolli, sub^p. n. 



Proportions and essential characters as in Ps. obesus, but 

 the general colour above, instead of being sandy, fawn, or 

 buffy, quite dark, as dark as Ridgway's " hair-brown," but not 

 matching that or any other colour owing to its dull yellowish 

 suffusion. Dorsal hairs all broadly tipped with black, partly 

 hiding their buffy or drab subterminal bands. The crown of 

 the head is particularly different from that of obesus, as the 

 hairs, buffy subterminally in both, are in the new form 

 broadly tipped with black. Below there is a similar darkening 

 of the general colour, the hairs being more or less tipped 

 with blackish. Ears, hands, and feet dull fawn. Tail buffy 

 on sides and below proximally, its upper surface with a 

 blackish line, of which the hairs lengthen terminally, with a 

 well-marked crest and terminal black tuft, the black extending 

 all round the distal third of the tail. 



Dimensions of the type (measured in flesh by collector) : — 



Head and body 178 mm. ; tail 149 ; hind foot 38 ; ear 14. 



Skull: greatest length 46'5 ; basilar length 38; greatest 

 breadth 26-8. 



Bab. Damietta, N. Egypt. 



Type. Old male. B.M. no. 8. G. 21.1. Collected 8 January, 

 1908, and presented by Mr. M. J. Nicoll. Four specimens. 



Mr. Nicoll saw considerable numbers of this animal, all of 

 the same dark colour. 



A similar instance of local blackening is given by Merriam * 

 in the case of certain of the mammals found on the black lava- 

 beds of the Little Colorado desert, the contrast in colour between 

 the specimens from the black soil and those of the desert 

 being such that full specific rank is given to an Onychomys 

 and a Perognathus, while a Citellus from the same place is 

 separated as a subspecies. 



* N. American Fauna, No. 3, pp. 59-60 (1890). 



