204 ]\Ir. O. Thomas on Mus Burtoni. 



specimen ; but as I had skinned tliis latter more than six 

 months before, the recollection is probably of little value. 

 The measurements have unfortunately been lost with the 

 skin, to which they were tied. 



" I know nothing of its habits ; but the natives say it occurs 

 only in the reed- and sedge-covered swamps, which are here 

 very numerous, owing to the windings of the stream." 



The Milk-dentition o/Aulacodus. 



In connexion with the working out of the above, an 

 examination of the teeth of Aulacodus at different ages has 

 been made, and this has been rewarded by the discovery, in 

 a foetal specimen about 110 millim. in length, with a basal 

 length of 34 millim., of minute and quite rudimentary milk- 

 teeth fixed in the gum just above each of the ])remolar3. 

 This discovery confirms the usually accepted homology of 

 the last-named teeth and also bears out the original sugges- 

 tion of Schlosser * that the milk-teeth are shed in extreme 

 youth, a suggestion which he afterwards unfortunately 

 withdrew in favour of the theory that there is an ordinary 

 tooth- change, the milk and permanent teetli being very like 

 each other, except that the lower milk-teeth are more com- 

 plicated than their successors. This error is evidently due to 

 his having been deceived by the great difference between 

 worn and unworn permanent teeth. This latter view is, of 

 course, now finally disproved. 



The contrast between Hystri.r, with its long persistent 

 "''■ ' ^, and AidacoduSy with its rudimentary and early shed 

 one, is very striking. 



Hensel f has recorded his failure to find any trace of rudi- 

 mentary milk-teeth in Phyllomys and Dactylomi/s, and, to the 

 best of my belief, they have not hitherto been observed in 

 any members of tlie subfamily Echinomyinai. 



XXI. — Xoteon'Mus Burtoni, T/ios. By Oldfikld Thomas. 



In the 'Annals' for 1892 J I described a West-African 

 mouse under the above name ; but Prof. T. TuUberg, of 

 Upsala, who has himself given a most excellent account § of 



* * ral;iH)iitograpliica,' xxxi. p. l^il (It'i'^o). 8ee nJso Foi-syth Major. 

 Atti Soc. Ital. XV. p. .") ( isn'). 

 t Abb. Ak. Beil. lS7i>. p. 5:5. 

 I (0) X. p. \S-2. 

 § " Ueber einige Muriden aus Kauieniii," Goji. Wi.ss. L'psala, I8i>3. 



