Dr. N. Severtzoff on the Mammals of Turkestan. 55 



must be sought for. I will also add that G. murinus is some- 

 what darker than A. arvalis. As regards the geographical 

 distribution of this hamster, only the two above-mentioned 

 localities are known, as I have not since then met with any 

 others. 



In the spring of 1864 I met with many A. arvalis on the 

 Irtish and Ishim. I examined them in search of cheek- 

 pouches ; but there were no G. murinus among them.] 



48. Meriones tamaricinus. 



Has been met with by me about the Lower Syr-Darja and 

 Lake Aral in the low plains, where it is a resident. 



49. Meriones tneridianus. 

 Range similar to that of the preceding species. 



50. Meriones optmus. 



A very common resident throughout Turkestan, except the 

 south-western parts. It keeps, however, always at low 

 elevations. 



51. Meriones [Rhombomys] collium^ n. sp. 



Is an intermediate form between M. oplmus and M. tama- 

 ricinus^ having the size and coloration of the latter and the 

 tail-tuft of the former ; but it is differently coloured from 

 either, and somewhat smaller. Here I give the comparative 

 diagnoses : — 



M. coUium. Supra rufescens, nigro irroratus, apicibus pilium nigris, 

 subtus albus ; cauda corpori concolor, fioccosa, bicolor, pilis ru- 

 fesceutibus et nigris intermixtis ; flocco etiam bicolori, fuliginoso et 

 canescente ; dentes incisores supra unisulcati. 



M. opimus. Supra pallide et sordide fulvescens, fuhginoso irroratus ; 

 Cauda praeter fioccum nigrum unicolor, intensius fulva ; dentes inci- 

 sores bisulcati. 



{M. lybicus). Ut M. ojnmus, sed incisoribus unisulcatis. 



M. tamaricinus. Ut if. collium, sed flocco caudse perparvo, psene 

 distincto, cauda unicolori fuliginosa. 



M. collium has the black tail-tuft surrounded by a pale grey 

 margin ; the hair of the latter is just as long as the black-tuft 

 hair. Length about 7-8 inches, tail 6^-7 inches. Obtained 

 on the lower spurs of the Semirechinsk-Alatau, between Koksa 

 and Hey, and also on the Karatau Mountains. In the latter 

 locality I obtained in June 1867 a young specimen, which 



