Mr. R. I. Pocock on Isometrus americanus (Linn.). 57 
hand; fingers sinuate and not proximally in con- 
tact when closed. 
The sexual characters of the male in this species are very 
variable. The above characters have been taken from speci- 
mens presenting the smallest amount of sexual variation. In 
others, such e. g. as the type of Jorcipula, these characters are 
much more marked. 
Of this species I have seen one female from Moyabama, 
one female from Demerara, three females and two males from 
Iquitos, two females and two males from Columbia. 
Isometrus androcottoides, Karsch. 
3g 9.—Third caudal segment with a median inferior keel in 
its hinder half; fourth with a median inferior 
keel almost throughout its length. 
? .—Pectines lobate. 
Tail not more than six times the length of the cepha- 
lothorax, parallel-sided or slightly thicker at its 
anterior extremity. 
Brachium very slightly thinner than hand; fingers 
not sinuate and in contact when closed. 
¢ .—Pectines not lobate. 
Tail more than seven times the length of the cepha- 
lothorax, parallel-sided; fifth segment of the 
same width throughout. 
Brachium about seven eighths width of hand; fingers 
not sinuate and in contact when closed. 
Of this species I have seen five males and four females 
without any locality, one male and two females from Deme- 
rara, one female from Trinidad. 
Isometrus insignis, sp. n. 
Colour.—Dull black above; hands, finger-tips, and under 
surface of the chele and legs with reddish tint; distal tarsal 
segments and pectines testaceous. 
Cephalothorax a little wider than long; anterior margin 
angularly excised; ocular tubercle situated in the anterior 
half, shallowly excavated, its sides feebly roughened, the 
roughness continuous in front with aseries of granules which 
extends towards the anterior margin; the posterior keels 
parallel, feebly granular, extending from the hind margin to 
a point about midway between this margin and the ocular 
tubercle ; space between these keels bearing a deep median 
