igiô.j 



Fauna of the Chilka Lake : Terrestrial Isopoda. 



465 



zealandiae. On the surface of the head, parallel to the posterior margin, is a narrow 

 furrow, making the posterior margin stand out distinctly, and there is a shallow and 

 less well-marked furrow running outwards and backwards on each side parallel to the 

 posterior margin of the eye. The side-plates of the first segment are completely 

 united with the central portion of the segment, no suture being noticeable ; in the 

 2nd, 3rd and 4th segments in the female, there is a distinct suture between the side- 

 plates and the central portion; in the 5th, 6th and 7th, the side-plates are again 

 united with the central portion without a distinct suture. In the male there is no 

 distinct suture even in the 2nd, 3rd and 4th segments, and only an indistinct line or 

 slight groove as in segments 5, 6 and 7. 



The question as to whether the side-plates are coalesced with the segments or 

 are separated by a suture is one that is not easy to decide without allowing the 



Ligia exotica, Roux. 



Fig. 7. — First maxilla of right side, taken from a male specimen with body 22 mm. long. 

 Fig. 8. — Left maxilla from same specimen showing four plumose setae on the inner lobe. 

 Fig. 9. — »Second maxilla. 



specimens to dry, and this is not always possible. There seems also to be consider- 

 able variation in this character in the different species, but there are a few cases 

 which appear to show that the difference between the male and female in this respect 

 holds for more than one genus of the Oniscoidea. For example, I have noted the 

 same thing in Deto aucklandiae (1915, p. 438), where the side-plates in segments 2, 3 

 and 4 are separated from their segments in the female by a suture, while in the males 

 they are quite continuous with the segments. In the other species of Deto, however, 

 there appears to be no suture even in the females. Again, in establishing the genus 

 Anomaloniscus , Dollfus (1893B, p. 187) gives as one of the chief characters, that 

 there is a suture between the side-plates and the segments in segments 2, 3 and 4 

 in the female, but not in the male. Apparently it is impossible to lay down a gene- 

 ral rule with regard to this sexual difference. Thus, though the difference holds in 



