VI CONTENTS 



Page 



Speciation and geographical variation 34 



Geographic variation in response to selective factors of the habitat . . 35 



Modes of speciation 36 



Sympatric speciation 37 



Geographic speciation 39 



Clinal variation 39 



Geographic isolates 40 



Zoogeographical considerations 44 



Effects of the Pleistocene on the dispersal of Saharan and Libyan 



rodents 44 



Zoogeographical relationships of the rodents of the Sahara and South- 

 west Asia 53 



Conclusions 61 



Systematic treatment 62 



Plan of treatment 62 



Gazetteer of principal collecting localities 67 



Family Cricetidae 69 



Subfamily Microtinae 69 



Genus Microtus Schrank 69 



Microtias mustersi Hinton 69 



Subfamily Gerbillinae 73 



Genus Gerbillus Desmarest 73 



Gerbillus aureus aureus Setzer 87 



Gerbillus aureus favillus Setzer 89 



Gerbillus aureus nalulensis, new subspecies 90 



Gerbillus eatoni eatoni Thomas 95 



Gerbillus eatoni inflatus, new subspecies 97 



Gerbillus eatoni versicolor, new subspecies 98 



Gerbillus gerbillus aeruginosus, new subspecies 103 



Gerbillus gerbillus discolor, new subspecies 106 



Gerbillus gerbillus gerbillus (Olivier) 109 



Gerbillus gerbillus latastei Thomas and Trouessart 110 



Gerbillus gerbillus psammophilous, .new subspecies 112 



Gerbillus pyramidum hamadensis, new subspecies IIS 



Gerbillus pyramidum tarabuli Thomas 121 



Gerbillus amoenus vivax (Thomas) 125 



Gerbillus campestris brunnescens, new subspecies 133 



Gerbillus campestris dodsoni (Thomas) 136 



Gerbillus campestris haymani Setzer 139 



Gerbillus campestris patrizii (de Beaux) 141 



Gerbillus campestris wassifi Setzer 143 



Gerbillus grobbeni Klaptocz 146 



Gerbillus henleyi henleyi (de Winton) 147 



Gerbillus kaiseri Setzer 149 



Genus Pachyuromys Lataste 153 



Pachyuromys duprasi natronensis de Winton 153 



Genus Merioncs Illiger 157 



Meriones caudatus amplus, new subspecies 165 



Meriones caudatus caudatus Thomas 169 



Mi r tones caudatus confalonierii de Beaux 172 



