64 



leB3 striped, it occurs on the sandy and stony plain which is 

 covered more or less with low thickets of bushes, and longish 

 grass. It is extremely rapid in its movements. 



In this male there are 170 ventrals and 141 caudals. The 

 variation in the ventrals of this species may be as much as 32, 

 the lowest number being IGl*, and the highest 195. In seven 

 specimens from Arabia the variation is only 17 ; but if one of 

 those from Maskat is excluded, the variation is only 11, the lowest 

 number being 168 and the highest 179. This exceptional speci- 

 men has 185 ventrals, and iu this high number it leads into the 

 representatives of the species found in Persin, Baluchistan, 

 Afghanistan, and Sind, which are almost invariably distinguished 

 by a high number of ventrals ranging from 182 to 194. Among 

 ten specimens from these countries, only one from Sind has its 

 ventrals falling as low as 177. On the other hand, 16 specimens 

 from Tokar, Suakin, and Durrur, have the ventrals varying from 

 163 to 174, but only in four does the number ri.^e above 169, 

 while in seven it does not exceed 166. The species, therefore, 

 in the Suakin district, is characterized by a lower number of 

 ventrals than in any other locality. 



In the lower part of the Valley of the Nile, the ventrals vary 

 from 168 to 177, but in Upper Egypt (Assuan) the number 

 rises to 195, while, in the extreme west of its distribution, the 

 high number 183 occurs at Biskra. 



This species and Psammophis Jeithii, Gthr., have sometimes 

 been mistaken the one for the other, and TapTiroitietopon lineo- 

 latiim, Brandt, has occasionally not been distinguished from the 

 latter. Their features are expret^sed by the following numbers : — 



P. sibilans 



P. sckoA'ari .. 



P. leithii 



T. lineolatum 



a 



158-198 

 163-194 

 170-185 

 175-194 



