202 Mr. O. 'Jliomas on a 



XX. — Description of a new Species of Reed-Rat (Aulacodus) 

 from East Africa, with Remnrhs on the Milk-dentition of 

 the Genus. By Oldfield Thomas. 



Among the mammals obtained by Dr. J. W. Gregory on his 

 recent expedition to East Africa are five specimens belonging 

 to the genus Aulacodus. Of these, four — a skin with its 

 skull, a separate skull, and two young specimens in spirit — 

 all obtained at Ngatana, on the Tana River, belong evidently 

 to A. swinderenia7ius*, Temm., the common species, which 

 is spread over the whole of the Ethiopian Region, from 

 Senegal to the Cape. The fifth specimen, however — a skull 

 alone — shows such differences from the others that I cannot 

 but consider it to represent a distinct species. It belonged 

 to a specimen obtained by Dr. Gregory in the Kikuyu 

 Country, near Mount Kenia ; but the skin was most unfor- 

 tunately stolen, so tiiat the only part which remains is the skull. 

 I propose to term the species 



Aulacodus gregorianus, sp. n. 



Size much smaller than in A. sivinderenianus, the differ- 

 ence especially well-marked in the molar teeth ; frontal 

 region broad and flat, not convex or inflated, but, on the 

 contrary, with distinct concavities just internal to the rudi- 

 mentary postorbital processes. Opening between the olfactory 

 and cerebral fossse much broader above than below, the con- 

 verse being the case in the other species ; this difference 

 appears to be due to the absence or reduction of the frontal 

 sinuses. Anterior palatine foramina penetrating less than 

 usual into the maxilla3, the most posterior point of the pre- 

 maxilla3, on the palatal surface, being exactly level with their 

 posterior margin. 



Upper premolar (Pi) with a small third external root raid- 

 way between the two main external roots, a character not 

 present in any of the fourteen skulls of A. swinderenianus in 

 the Museum. Upper incisors with the innermost of the four 

 spaces between the grooves rather broader and the outer 

 much narrower than in the ordinary species; in fact, in 

 A. swinderenianus the part of the tooth outside the outermost 

 groove is nearly equal to the whole remaining portion, while 

 in A. gregorianus the same part is but little broader than the 

 next section, between the outer and middle grooves. 



* 'I'liis nuine has <;i"nerally been misspelt either a;s swinderianui (the 

 ox'v^umA) ov !>ivindi'rii>aiuis : but as Temniinck distinctly states that it is 

 nanu'd in lionour ot" riof. van Swindoron, the proper form is clearly a« 

 above. 



