14 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
ratlier limited, and the only Memoir dealing with Antarctic Sipunculids is Theel’s Report 
of the Swedish Expedition. It does not fit into any of the species therein described? 
nor with those of Michaelsen. 
I therefore take the opportunity of associating with it the name of Sir Douglas 
Mawson. 
The general appearance of this species is very different from the preceding, both 
in its creamy white colour, in the texture of the skin, and in the general form of body. 
Although these differences are rather difficult to put into writing, yet when the two 
species are seen side by side the distinctness is quite evident. 
A characteristic feature is the presence at the rounded hinder end of the body of 
a definite cone, low and rounded (fig. 3). In the extended condition of the animal this 
is prominent, but when the animal is more or less contracted, this cone, while still 
retaining its definite form, becomes sunk into a fossa, shallow or deep according to the 
degree of contraction (figs. 4, 5). Sometimes the cone is sunk to such a depth that it 
is invisible from the side. 
It is a feature that is not unusual in the genus Dendrostoma, if one may judge 
from the figures illustrating the Memoirs of Selenka and of Ikeda, though it does not 
appear in such a definite form in any species of Pliascolosoma. 
The tentacular crown, however, has the usual arrangement of the latter genus. 
There is a cushion on the dorsal surface, grooved lengthwise so as to appear double, 
and around the mouth, which lies excentrically, is a circle of thirty short tentacles : 
these are connected at their bases in couples, one couple is median ventral, the rest 
lateral; actually there are fifteen such couples (figs. 9, 10). 
In a series of transverse sections through the crown I was unable to detect any 
cerebral canal. There certainly is nothing like that figured by Herubel for P. charcoti 
(1908, p. 5, figs. 5, 6). 
The animal attains a length of 42 mm., which is The largest in the collection. 
This figure includes the fully extended introvert. The shortest individual is only 8 mm. 
in length. 
A specimen measured gives the following figures :—Total length, 39 mm., of 
which the introvert occupies 20 mm., taking the anus as its point of origin. The diameter 
of the body is 5 mm., while that of the introvert is only 2 mm. Thus the introvert is 
rather longer than the body, and is distinctly marked off from it by its sudden decrease 
in diameter. 
In the following table I give measurements of other individuals in which the 
introvert is fully extended, and it will be seen that the amount of contraction of the body 
is very unequal, especially at the hinder end, hence the comparative uselessness of these 
proportions as a specific character. 
