AMPHIPOUA— STEBBING. 625 



species had beeu named in this genus, it really contained only one, 

 which in that case must be called Iciliiis ovalis, Dana. In the 

 meantime, however, examination of various specimens collected 

 by the "Thetis " Expedition has led me to a different conclusion. 

 The grounds on which this change of opinion rests will now be 

 explained. Unfortunately it cannot even now lay claim to 

 finality, because the earlier descriptions suffer from obscurity or 

 incompleteness, and among the newly acquired specimens of these 

 fragile animals not a single one was pei'fect, not only every 

 individual wanting some of its parts, but some of the parts being 

 absent from the whole collection. 



It should be borne in mind that Professor Haswell, who in 

 1880, figured and described two Australian species, first /. aus- 

 tralis and then /. punctatus, in 1882 united them, i-emarking that 

 " an examination of a series of specimens has made it appear 

 probable that /. australis and /. jninctatus are to be regarded as 

 varieties of one species." He had previously stated that /. j^unc- 

 tatus was " distinguished from /. australis chiefly by the greater 

 breadth of the rami of the three posterior pairs of pleopoda" 

 [uropods]. It remains doubtful whether in combining his two 

 species he was influenced by any other character than this. 



When instituting the species /. dance in 1888 for a female 

 specimen taken at a depth of 33 fathoms off Melbourne, I pointed 

 out the feature distinguishing it from Dana's typical I. ovalis 

 taken in 31 fathoms north of Borneo. These gain a new impor- 

 tance from the steadfastness of character in the " Thetis " 

 specimens which agree with the account of /. daiue. I do not 

 wish to deny that future discoveries may once more unite /. ovalis 

 and /. dance, but I think it extremely improbable that such a 

 union can be effected between /. ovalis and /. australis. In the 

 existing state of knowledge the following synoptic table may be 

 offered : — 



f First and second pleon segments with hind 



I margin acutely produced at the 



1 middle— 2. 



^ j First and second pleon segments with hind 



I margin not acutely produced at the 



L middle— 3. 



rLast segment of peraeon without, third 



I segment of pleon with, acute process 



J at middle of hind margin I. Icilius ovalis, Dana. 



^ ; Last segment of peraeon with, third seg- 



' ment of pleon without, acute process 



L at middle of hind margin 2. Icilius dance, Stebbing. 



r Poster o-lateral margins of first and second 



pleon segments forming two strong . ,. „ 



• teeth ^- Icthus auatrahs, HASweU. 



^ i Postero-laterai margins of first and second 



pleon segments forming no strong , , „ „ 



^ teeth .. i. Icihus punctalu3,B.aAwcU 



