Swamp-Rats of East Africa. 153 



may be taken for tliis species also, as in general colour the 

 two forms are exactly the same. 



Skull larger and heavier ; molars considerably longer, m^ 

 witli 6 well-defined laminse. Lower incisors exactly as in 

 denti, i. e., with only one groove. 



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



Head and body 159 mm. ; tail 101 ; hind foot 28*5 ; 

 ear 22. 



Skull: greatest length 40*5; basilar length 33"3 ; condylo- 

 incisive length 38*2 ; zygomatic breadth 21 ; interorbital 

 constriction -4 ; squamosal breadth of brain-case 15'7 ; length 

 of nasals 1G*3 ; greatest width across expanded part of 

 nasals 7 ; breadth across middle of nasals (taken just behind 

 the anterior expanded portion) 4*7 ; depth from highest point 

 of orbit to alveolar border at front of vi^ 12"2 ; palatilar 

 length 19"2 ; length of palatal foramina 7*8 ; postpalatal 

 length 14'1; length of upper molar series, from anterior 

 alveolar border to back of last molar, 8'9 ; length froui 

 anterior enamel-base of Hi' to back of m^ 8"5 ; greatest width 

 of in} 2*5. 



Ifah. Burunga, Mt. Mikeno, Congo Beige. Altitude 

 6000 feet. 



Ti/pe. Old male. B.M. no. 11. 12. 3. 110. Original 

 number 2206. Collected by Mr. Robin Kemp on June 6th, 

 1911. 



The 6 laminse of m^ immediately separate this form from 

 the Ruwenzori denti. 



Mr. Kemp obtained in all a dozen specimens of this inter- 

 esting Otomys, six from the type-locality and six from 

 Buhamba, near Lake Kivu, Congo Beige. 



Division B. 



Lower incisors -with one deep outer groove and one very shallow inner 

 groove. Ventral surface of tail light. 



Section I. 



The members of this section all possess skulls exhibiting a marked arched 

 appearance, the interorbital region being conspicuously elevated and 

 the nasals and brain-case so depressed as to accentuate this humped 

 or arched character. (This condition is also found in Division U, 



Section I.) 



Group 1. 

 m^ with 7 laminae. 



(3; Otomijs thomasi, Osg. 



Otomys thomasi, Osg. JTield Mus. Nat. Hist. Publication, Ml, Zool. 

 Ser. vol. X. no. 2, p. 9 (1910). 



This species is immediately known by its curious arched 



