522 ME. E. I. POCOCK ON THE AEACHNIDS COLLECTED [Juoe 21, 



Palpi — femora claA-ate, furnished with a few short spines and 

 short hairs ; tihia narrower at the base, armed below throughout 

 its length with man}' short spines ; protarsus distally narrowed, 

 armed below, like the tibia, with many short spines. In addition 

 to the normal spine-armature, there are a few lougish spines on 

 the upperside of the basal segments of the legs. 



Terijal plates of abdomen and of thorax beset with short spines, 

 of which there is a distinct posterior row. 



$ . Xot very different from the male in length of limbs, size of 

 mandibles, &c. ; but with shorter malleoli ; mandibles and head 

 spiny ; thorax, abdomen, tibia and protarsus of palp, and basal 

 segments of legs not spiny ; mandibles strongly toothed, second 

 tooth twice as long as the first and twice as long as broad, third 

 and fifth teeth small and subequal, fourth tooth large, but shorter 

 than the second ; inner row of teeth consisting only of two, one in 

 the same position as in the male, the other considerably lower. 



Measurements in millimetres of type ( S )• — Total length of trunk 

 14, with mandibles 17'8 ; length of palp 19, of 1st leg 12, of 2nd 

 leg 11-5, of 3rd leg 17, of 4th leg 2(3 ; tibia of palp 6, protarsus 

 and tarsus 6 ; tibia of 4th leg 6, protarsus 5 ; width of head- 

 plate 4-5. 



2 . Total length of trunk 16, with mandible 21 ; width of 

 head 4-8 ; length of palp 18, of 1st leg 11, of 2nd 12, of 3rd 15, 

 of 4th 26 ; tibia of palp 6, protarsus and tarsus 5*5; tibia of 4th 

 leg 5-5, protarsus 4-5. 



Loc. Maziwa Mitatu in the Taru desert {type') ; examples also 

 obtained at Machuma in the Taru desert, Mbuyuni and Ndi 

 (Weiss Eoad). 



The two known species of this genus may be readily distingiushed 

 as follows : — 



a. Length of trunk 25 mm. ; terminal fang of upper jaw 

 projecting a very short distance beyond the flagellum, 

 its second tootli much larger than the rest ; a row of 

 5 stout spines near the base of the flagellum on the 

 inner side ; filiform terminal part of flagellum long, 

 far surpassing the membranous basal portion ; head, 

 mandibles, upper surface of body, and bases of limbs 

 studded with stout bristles, not spines ; femora and 

 tibice of posterior legs black bicolor Poc, cJ. 



h. Length of trunk 15 mm. ; terminal fang of upper jaw far 

 surpassing flagellum, the second tooth not larger than 

 those behind it ; only two spines near the base of the 

 flagellum on the inner side ; filiform portion of 

 flagellum scarcely surpassing the membranous basal 

 portion ; head, mandibles, and dorsal surface of trunk 

 studded with spines ; posterior legs with only the 

 distal end of the femur black spinulosa, sp. n. 



Genus Biton Karsch. 



BiTON TiGRiNUM, sp. n. (Plate XLII. figs. 14, 14 a.) 



Colour reddish yellow, variegated with deeper brown ; head-plate 

 pale in its middle third, brown at the sides, tubercle black ; 



