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 oi forcipula^ 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. 



(J ? . — Third caudal segment with a median inferior keel in 



its hinder half; fourth with a median inferior 



keel almost throu2;hout 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 ceplia- 



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 Derae- 

 rara, one female from Trinidad. 



Isometrus insignis^ sp. n. 



Colour. — Dull black above; hands, finger-tips, and under 

 surface of the chelse and legs with reddish tint ; distal tarsal 

 segments and pectines testaceous. 



Cejohalothorax 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 a series 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 t!ie ocular 

 tubercle ; space between these keels bearing a deep median 



