276 Transactions. 



Colour.— Whitish. 



Length — cephalon, 2 - 5 mm. ; pereiou, 8 - 5 mm. ; pleon, 6 - 5 mm. 

 Depth — pereion, 2 mm. ; pleon, 3 - 5 mm. 



Rob. — Fresh-water lagoon on Ruapuke Island. 



The description given above applies to the Ruapuke Island 

 specimens. Those from the neighbourhood of Dunedin differ 

 considerably in general appearance, having the segments of the 

 pereion longer, so that the appendages are more separated, 

 and there are also some minor differences. I was at first in- 

 clined to consider them as a separate species, but the resem- 

 blances in the appendages are so close, and the differences rather 

 in the proportions of the body — characters difficult to estimate 

 precisely, and perhaps partly due to shrinkage caused by the 

 preserving-fluids used — so that I propose to consider them as 

 a variety. 



Phreatoicus kirkii, var. dunedinensis, nov. var. 



Differing from the type in having the segments of the pereion 

 rather longer, more slender, and more separated ; the dorsal 

 surface of body, especially of the last segment of pleon, with more 

 numerous setse ; pereiopocla more slender, the basa of the last 

 three pairs less expanded. 



Colour. — Whitish. 



Length — cephalon, 2 - 5 mm. ; pereion, 13 mm. ; pleon, 7 mm. 

 Depth — pereion, 2 mm. ; pleon, 3-5 mm. 



Hob. — Streams at Mosgiel and Woodhaugh, near Dunedin. 



Mr. Sayce has laid considerable stress on the proportion of 

 the length of the pleon to that of the cephalon and pereion 

 combined in the various species of Phreatoicus and allied genera. 

 If we take the measurements given above and work them out 

 as Mr. Sayce has done we find that in the typical specimens 

 the pleon is t ^q of the combined length of cephalon and pereion, 

 while in the variety dunedinensis the corresponding fraction 

 is only ££$, the difference being thus considerable. Measure- 

 ments of this kind are, however, not easily made with the same 

 accuracy in all cases, and they vary to some extent in different 

 individuals, a?id certainly these fractions in the present instance 

 would lead one to think that the specimens from the different 

 localities differ more than they really do. 



It will be seen that the present species is very closely allied 

 to P. assimilis, and that in the lower lip and the inner lobe of 

 the first maxilla it agrees with this species and with P. australis 

 and P. skephardi, and differs from P. typicus. 



In the structure of the last segment of the pleon, and in some 

 other points, it may be considered to be intermediate between 

 P. australis and P. assimilis. 



