190 Tra7is actions. — Zoology. 



tion of Palinunis in fcavour of Professor Hutton's theory^'' of 

 an antarctic continent, from which the great southern land- 

 masses were stocked. 



It appears from Miers's " Eevision of the Idoteidce " that 

 there are only five distinct species recorded from Britain, and 

 four, with a doubtful fifth (I. viargaritacea), from Australia, so 

 that, according to our present knowledge, the group is better 

 represented in New Zealand. It must not, however, be assumed 

 that our knowledge of the New Zealand forms is by any 

 means complete. Thus, Idotea festiva and Cleantis tubicola 

 are known from single specimens only, and I have in addition 

 a specimen from Lyttelton, which, though too small and im- 

 mature for identification, certainly does not belong to any of 

 the recorded New Zealand species, but appears to come nearer 

 to Idotea acuminata. 



I have dissected and examined the three species, I. lacus- 

 tris, I. ungulata, and I. clongata, in some detail, but the 

 results are not sufficiently important to justify a minute 

 description of their difi'erent parts. It is, however, evident 

 that I. ungulata and I. clongata are both much more special- 

 ised than 1. lacustris, and depart further from the parent 

 species from which the Idoteidce are descended. Thus, in 

 them the segments of the postabdomen are more anchyiosed 

 together; the epimera are not so well developed, and are more 

 or less joined to their respective segments ; tliere is no trace 

 of the second ramus articulating with the basal plate of the 

 operculum, and the same tendency is seen in the mouth parts. 

 Of the two, again, I. elongata is more specialised than I. ungu- 

 lata. I. peronii appears to come near to the latter species, 

 but I have not examined it in such detail. 



It is perhaps worth while drawing attention to the fact 

 mentioned below, that the coalescence of the segments of 

 the postabdomen is subject to considerable variation in the 

 same species, and tliat hence the number of segments of the 

 postabdomen, though a useful character for dividing the 

 species into artificial groups, cannot be relied upon very far to 

 indicate the natural affinities of the different species. 



After some consideration, I have decided to give full 

 descriptions of all the species. Most of these have already 

 appeared elsewhere, but they are somewhat scattered, and 

 are not easily accessible to New Zealand students. Those 

 which are not original are placed in inverted commas, and 

 have the author's name given at the end in brackets. 



I have not attempted to give the full synonymy, but I have 

 endeavoured in each case to give those references which will 

 be required by New Zealand students, and also the reference 



* " N.Z. Journal of Science," vol. ii., p. 1. 



