26 W. :\I. TATTRRSALL. 



of the basiil joint without setm, liut armed witli twenty-one stout spines increasing in 

 size posteriorly. 



Length of adult and ovigerous female, 20 mm. from the eyes to the tip of the 

 telson. 



Colour of preserved specimens light brown, with a broad band of dark brown 

 pigment across the dorsal surface of the first segment of the pleon and scattered 

 patches of dark pigment on the lateral parts of the carapace, basal joints of the 

 antennules and antennae and the basal membranous pad of the eyes. 



One of the specimens has young, considerably advanced in development, in the 

 incubatory lamellae. 



In both specimens the telson is considerably damaged, and the description and 

 figures have been drawn up from both specimens and fragments of the telsons found 

 along with them. This fact must be borne in mind in dealing with specimens of this 

 species which may be found by future expeditions. It was a matter of considerable 

 surprise and no little interest to find in this collection two specimens belonging to 

 a genus hitherto known only from a single specimen from Greenland and two taken 

 off the cost of Ireland. 



There can be no doubt that //. antarctica is co-generic with //. fyllse (Hansen, 

 1887). All the distinctive characters of generic importance in the mouth parts and 

 thoracic limbs of the latter are reproduced in //. antarctica down to the minutest 

 detail. The points of difference between the two species are, however, sufficiently 

 well-marked and numerous enough to justify specific separation. They may be pointed 

 out as follows : — 



H. antarctica is in general build a more robust and less fragile species than 

 //. fyllse. 



Antennae. — In H. fyllse the terminal joint of the peduncle is longer than the 

 penultimate, whereas in //. antarctica the reverse obtains. 



Antennal scale.— In II. fyllse the outer margin bears only five spines, between 

 which are numerous setsB. In H. antarctica, on the other hand, there are eleven spines 

 on the outer margin and no setje between them. 



Telson. — The telson in Hansen's type-specimen was broken, but so much of 

 it as remained showed that the armature consisted of both spines and setfe. In 

 //. antarctica the telson is armed with spines only, which are probably more numerous 

 tlian in //. fyllse. The shape of the telson in both species is also somewhat divergent. 

 That of //. antarctica recalls rather markedly the telson of Petalophthalnms armiger as 

 figured by Sars in the ' Challenger ' Report. 



Outer uropods. — //. fyllw lias the outer uropods armed with both spines and 

 setse, whereas in //. antarctica there are spines only present. The spines in II. fyllai 

 number six, while in //. antarctica there are twenty-one. 



Fleopods. — The type specimen of //. fyllai had only one pleopod remaining. This 

 was one of the third pair, and is described by Hansen as biarticulate. Presumably, 



