106 AUSTRALASIAN ANTARCTIC EXPEDITION. 



Previous authors have noted the readiness with which the hinder segments break 

 away, owing to the extremely slender connections between them, so that the true 

 dimensions of the species is unknown. 



It is almost colourless, except that in front of the chaetaa of each of the segments 

 4-10 is a pinkish area occupying more than half the length of the segment. This is the 

 " anterior glandular band " of Arwidsson, with which the indistinct " posterior band " 

 is continuous. There is no need for me to add anything to Arwidsson's exhaustive 

 study of the species. 



Locality. 



Commonwealth Bay, Boat Harbour, 3J fathoms. 



Distribution. Cape Adare, Victoria Land (Willey); Port Charcot and Peter mann 

 ( Gravier) ; S outh Georgia ( Arwi dsson) . 



Remarks. It is thus circumpolar. 



Genus ISOCIRRUS Arwidsson. 



ISOCIRRUS YUNGI Gravier. 

 Gravier (19 11), p. 122, pi. IX., fig. 109; pi. X, figs. 115-120. 



Gravier's type specimens were two fragments, of which one was an anterior 

 portion and the other a short piece of the hinder end. They are a good deal smaller 

 than the specimens collected by the " Aurora," and the tube in which the animal lived 

 was not collected or reported upon. 



Eleven individuals of the species, mostly imperfect, were obtained at a depth of 

 157 fathoms. In most of them the body is encircled by a portion of the mud-tube, 

 which has a very thick wall; thus a worm measuring 7 mm. in diameter fills the lumen 

 of a tube whose external diameter is 11 mm., so that its thickness is 2 mm. 



A complete individual studied is 110 mm. in length with a breadth of 5 mm. 

 anteriorly. Another one, lacking only the anal funnel and a portion of the long preanal 

 segment, attains a length of 135 mm. with a breadth of 7 mm.: but judging from some 

 of the fragments still within their tubes, the species may reach even a greater size than 

 this. 



The colour is almost uniform pale brown, except that in one or two cases the 

 5th and 6th segments are darker than the rest; the glandular band at the commencement 

 of the segments is nearly white. 



The complete individual first mentioned above consists of the " head," followed 

 by nineteen elongated chsetigerous segments and a long preanal segment ; this bears six 

 glandular half-rings, corresponding in position to the uncinal glands to be described 



