54 Rev. T. Hincks on the 
raised, contracted, suberect, forming a neck which bears the 
orifice ; orifice suborbicular, a small mucronate projection in 
the centre of the lower margin, the rest of the peristome occu- 
pied by 6-10 tubular spinous processes, a denticle within the 
peristome on the lower primary margin. Avicularia none. 
Owcium (fig. 36) rounded, developed behind the neck-like peri- 
stome (the orifice, with its full armature of spines, rising before 
it), sometimes traversed by a number of the immersed tubules. 
Primary cell (fig. 3 a) small, ovate; aperture occupying about 
two thirds of the front surface, surrounded by a raised border, 
which bears about 8-10 spines; the orifice nearly semicircular, 
occupying the upper portion of the aperture, the lower part 
closed in by a delicate membrano-calcareous covering; por- 
tion of the cell below the aperture smooth and solid. 
Zoartum forming very large cream-coloured crusts on shells. 
Extremely abundant; probably the commonest species 
amongst Dr. Dawson’s dredgings. 
[Bass’s Straits (Capt. Cawne Warren).] 
I have ranked this interesting form as a variety of MW. 
spinosissima, a species which I have described and figured in 
my report on the Polyzoa of Bass’s Straits (‘ Annals ’ for Aug. 
1881). In all the principal elements of structure there is an 
exact correspondence between the two; but there are also one or 
two differences, which materially affect the general appearance, 
and, at the first glance, few probably would be likely to iden- 
tify them. In the present variety the cells are very much 
larger than those of the Australianform. The latter are small 
and delicate, while those of the variety major are ample, 
broadly ovate, massive, and strongly built. But the chief 
difference between them lies in the system of tubules, more 
or less immersed in the cell-wall and showing as white striz 
on the glossy surface, which gives so distinctive a character 
to the North-Pacific form. Of this tubular structure I have 
been unable to detect any trace in the Australian specimens 
which I have examined. Possibly the condition of the stony 
crust may be such as to conceal it; but this hardly seems 
probable, as in the finest colony which has come under my 
notice calcification has evidently not proceeded far. It may 
also be noted that the cells of the Australian variety have a 
well-marked row of punctures round the margin. 
At present, looking to the close structural agreement be- 
tween the two forms, and in the absence of any precise know- 
ledge as to the development and function of the tubules, I 
prefer to include them in one specific group. 
The tubules appear as delicate white lines through the 
subhyaline crust, radiating from the circumference towards 
