170 Mr. R. I. Pocock on the Genus Urodacus. 



Concerning the latter point, so far as I am aware, the 

 occurrence of this form has hitherto never been reported from 

 any place outside the Australian continent ; and within the 

 limits of this area no locality of smaller dimensions than West 

 Australia has ever been assigned to a specimen of it. 



It will therefore be of interest to state that in the National 

 Collection there are in the first place four specimens from 

 Ceylon ; and in the second place, that of the Australian speci- 

 mens, while two are ticketed merely W. Australia, three are 

 from the Swan River and one from Port Lincoln. 



With regard to the sexes of this species, I do not know 

 that any difference between the two has ever been pointed 

 out. At all events Count Keyserling makes no mention of 

 the existence of any sexual features. But in the series of 

 this species that I have examined two very distinct forms are 

 to be noticed — the one possessing larger pectines and a longer 

 tail, the other smaller pectines and a shorter tail ; and, in the 

 absence of any direct evidence of the fact, I judge from 

 analogy that the specimens presenting the former character- 

 istics are males and that those presenting the latter character- 

 istics are females. 



The two may with certainty be distinguished as follows: — 



Male. — Cephalothorax as long as the first caudal segment 

 + two thirds of the second ; tail about four and three 

 quarter times as long as cephalothorax; pectines pro- 

 jecting considerably beyond the distal margin of the 

 coxal segment of the posterior pair of legs ; pectinal 

 teeth 19-22. 



Female. — Cephalothorax as long as the first and the second 

 caudal segments; tail about four times as long as 

 cephalothorax ; pectines not projecting so far as the 

 distal margin of the coxal segment of the posterior 

 pair of legs ; pectinal teeth 12-14. 



Count Keyserling's figure and description are without 

 doubt taken from a small female specimen. The length of 

 it is 54| millim., whereas the average length of the adult 

 females that I have seen is about 70 millim. 



Urodacus excellens, sp. n. (PI. VIII. figs. 2, 2 a.) 



Cephalothorax with a conspicuous circular incision in the 

 middle of its anterior margin, marked throughout its length 

 by a median sulcus, Avhich behind dilates into an equilaterally 

 triangular depression. The right and left portions of the 



