On tierhils referred I o the Genus Mciioncs. 20.'^ 



XX\'l. — yoteaon Gerhils referred to l/ie Genus Merioiies, loit/i 

 Descriptions of new Kipecies and ISnispecies. By Oldfield 

 Thomas. 



(Published by pertuissiou of tbe Triistoea of the British Museum.) 



Tiiii genus Meriones has long been in a very great state of 

 conl'usion, partly owing to the carelessness of authors in 

 hinijjing specimens Ironi all sorts o£ localities together, and 

 partly to the tact that t!ie genus falls into groups distin- 

 guishable only by the diiterent siises of their bullaj, and that 

 members of each of the groups may be found living side by 

 side — so that a single district may contain two or three 

 species, all looking so alike as to be reatlily confused with 

 each other, and yet really distinguishable on close examina- 

 tion. Thus no less than three species are found in Egypt, 

 the very country where certain names have been overlooked 

 or misapplied — so as to add to the general confusion. 



I have not been able to complete the work in any sense, 

 but can make some preliminary observations on the habitats 

 iu\d characteristics of the dift'erent forms. 



The bulhe, whose structure and development give the 

 j)rimary means of distinction, enable us to separate the species 

 (apart from tiie aberrant calurus and hurrianw) into four 

 groups, as follows : — 



(a) The bullae very large, the swelling in front of the 

 meatus projecting in front of the level of the hindmost corner 

 of the zygomata, and the suprameatal triangle also very 

 large. Meatal length (/. e. the distance from the back of the 

 bulla to the front of the meatal swelling) approximately 

 14-1.5 mm. 



(/') Bullte similarly large, but the suprameatal triangle 

 comparatively small. (Tail usually more bushy than in other 

 sj)ecies.) 



(o) Bulla3 smaller, the front side of the meatus little 

 swollen, and not reaching to the level of the zygoma (meatal 

 length about 11-12 mm.) ; triangle also small. 



((/) Bullaj quite small for the genus, almost in normal 

 jiroporfion to the general size of the skull. (Meatal length in 

 M. bladder i &2 mm.) 



In Algeria the contusion of the names is too great to clear 

 up now, but as a preliminary it may be said that north of the 

 Atlas we have true shawi (group c), which is represented on 



18* 



