Mr. R. I. Pocock on Neotropical Scorpions. 81 
posteriorly and terminating in an enlarged denticle, the latter 
strong and complete, terminating in front with a rounded 
tubercle and behind with an acute tooth in the first three 
segments; these three segments granular and obsoletely cari- 
nate laterally ; the inferior and infero-lateral keels entirely 
absent on segments 1-4, which are smooth and polished, the 
fourth being merely weakly granular beneath; the fifth 
segment deeply excavated above and widely so behind, with 
elevated granular lateral edges, the lateral surface weakly 
granular, the lower surface thickly and coarsely granular, 
convex and not carinate, the lateral keels merely represented 
by a series of few coarser granules behind; vesicle depressed, 
narrower than the fifth segment, carinate at the side, coarsely 
serially but not closely granular below ; a median series of 
small spiniform granules beneath the aculeus, the posterior 
of these the largest; the aculeus lightly curved from the 
base. 
Palpi moderately robust ; the humerus with its upper sur- 
face smooth, the anterior and posterior keels weak and weakly 
granular, the anterior surface also very feebly granular and 
defined below by a weakly granular keel; brachiwm smooth 
and rounded above and behind, its anterior surface defined by 
a keel above and below; manus wider than the brachium, 
smooth, rounded, not carinate, with scarcely even a trace of 
keel to define the hand-back; the length of the hand-back 
greater than the width of the hand, but less than the length 
of the movable digit; digits slender, moderately elongate. 
Legs slender, elongate, smooth, with two spurs at the base 
of the feet and the distal end of the posterior surface produced 
into a short acute process, just in front of which there is a 
long series of short minute spinules. 
Pectines moderately long, furnished with 10-11 teeth. 
Measurements in millimetres.—Total length 26°5, of cara- 
pace 4, of tail 16, width of first caudal segment 2°8, of fourth 
2°6; length of segments 1+2 33; width of the vesicle 2, 
width of brachium 1°3, of hand 2; length of hand-back 2°5, 
of movable digit 3°5. 
Loc. British Guiana (W. L. Sclater). 
Two adult female specimens. 
HETEROCHACTAS, gen. nov. 
(Pl. V.. fig. 6 Gras) 
The anterior border of the carapace rather deeply and 
abruptly emarginate in the middle line, with its lateral 
portions rounded and the anterior lateral eye scarcely at all 
