THE ZOOLOGIST. 



THIRD SERIES. 



Vol. XV.] JANUARY, 1891. [No. J69. 



ON the IDENTITY and DISTRIBUTION of the IRISH RAT, 

 MUS HIBERNICUS, Thompson. 



By Wm. Eagle Clarke & Gerald E. H. Barrett-Hamilton. 



Some amount of uncertainty, or of misapprehension, appears 

 to have always enshrouded the Rat described by Wm. Thompson 

 (Proc. Zool. Soc. 1837, pp. 52, 53), as the Irish Rat, Mus hibernicus. 

 The present contribution gives the results of investigations under- 

 taken with a view to the solution of this little problem. 



From Thompson's time to the year 1888 no practical atten- 

 tion appears to have been paid to this animal by zoologists ; 

 at least, no information based upon an examination of specimens 

 has, we believe, been contributed to a further knowledge of it. 

 On the other hand, the several naturalists who have had occasion 

 to refer to M. hiberuicus have ventured opinions as regards its 

 identity which are irreconcilable with the facts. 



In the course of this enquiry we have examined no less than 

 fifty-six specimens, of which forty were received in the flesh. As 

 the result of this investigation, based as it is upon an ample 

 supply of material, we are able to declare, without qualification, 

 our conviction that Mus hibernicus is a melanistic form of Mus 

 decumanus. Though only common in Ireland, less so in the 

 Outer Hebrides, and apparently unknown elsewhere in Britain, 

 there is no reason for regarding it as a distinct species.* For 



* De Selys Longchamps, in the Appendix to his 'Etudes de Micro- 

 mammalologie ' (1839), states that, if the colour of the fur is constant, and if 

 ZOOLOGIST. — JAN, 1891. u 



