92 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
It is very similar to the Northern Thelepus cincinnatus Fabricius, as Willey has 
pointed out, with which indeed he suggested that it is conspecific. But there appear 
to be a few differences from that Northern form, which has recently been described at 
length by McIntosh (1915, p. 26). 
Under the circumstances, it seems worth while to give the essential facts about 
the worm. 
The animal grows to a large size, frequently attaining a body length of 140 mm. 
or even more (in one specimen it reaches 190 mm.). To this length of body must be 
added that of the tentacles, which measure some 30-40 mm., though of course they are 
much coiled and contracted, so that in life they must exceed this measurement. 
Idle number of segments is 90-100 ; the diameter of the worm first mentioned is 
7-5 mm. 
The sides of the body are thick, rough, brownish, and very glandular ; and this 
is continuous with the large ventral gland shields. 
The cephalic collar or platform which bears the tentacles, carries numerous 
eye-spots over its entire extent. 
There are two bunches of gill filaments on each side of segments 2 and 3, which 
latter is also the first chsetigerous segment. Each bunch consists of a single transverse 
row of simple unbranched filaments—about 15 in a row on each side in the first gill— 
leaving a small gap in the median dorsal line equal to about the width of three filaments. 
The anterior gill extends downwards to below the level of the notopod. The second gill 
is smaller, and consists of some twelve filaments, and the dorsal gap is slightly wider. 
In twenty-five individuals, taken at random out of a jar containing more than one 
hundred, every one had two pairs of gills. Not one of all those examined showed any 
variation in this respect, which seems to justify the use of the genus Thelepus for two- 
gilled forms, or at any rate to refute the idea that variation in this matter commonly 
occurs in a species. 
The first notopod occurs on the third segment and is repeated on every segment 
throughout the worm, though in the hinder ones the number of chsetge becomes much 
fewer (in T. cincinnatus , McIntosh states that the notopod is absent in the last forty 
segments). The first neuropod lies in the 5th segment. It is of considerable extent, 
reaching down to the margin of the gland shield. But after the 10th segment it begins 
to dwindle in height and at the same time to project outwards, so that by the 20th 
segment the neuropod has quite a short vertical extent not more than twice that of 
the notopod, and so remains throughout the greater part of the animal, as oar-like 
appendages. 
The margin of the anterior neuropods is darkly pigmented. The chsetse of the 
first notopod and of those that follow are of two kinds, as in T. setosus. 
