92 
from the supramarginals, except the last three or four, by intermediate 
plates, of which there are at the base of the arms 4 or 5 longitudinal 
rows, or, in large specimens, even 6 or 7 such plates. The madreporite, 
which varies in size and shape, is situated about 4 r. from the centre. 
The marginals are covered with small, short, rounded tubercles similar 
to those on the abactinal plates. 
In each interbrachial area is an unpaired marginal plate, rather 
larger, as seen from above, than its immediate neighbours. 
The marginals are approximately of equal size throughout the 
length of the row, but very gradually decrease towards the tip. The 
number of supramarginals varies with the size; the inframarginals 
agree in number with them. In the largest (R. = 76) there are 32 
marginals from the tip of one arm to the tip of the next. In the 
smallest specimen measured (R. = 58) there are 24. 
The actinal plates are in contact, there being no papule; they are 
more or less polygonal in outline, and bear tubercles of the same cha- 
racter as the abactinals. The number of plates in the interbrachial 
area varies with the size from 7 to 10 between the oral angle-piece 
and the inframarginal. 
The adambulacrals carry 6 spines in 3 pairs (sometimes a fourth 
pair is present near the mouth) : these are stout, cylindrical, or some- 
what prismatic, with rounded ends; the innermost are the largest, 
and arch over the groove like the rafters of a roof; the outermost 
are shortest. These last are longer than the tubercles of the disc, 
and so stand up above the general level of the lower surface. 
The oral angle bears a couple of long, cylindrical, glassy-tipped 
dental spines, directed aborally, and in all the specimens lie prone 
on the parent plate (see Farquhar, 1897, pl. xiv, fig. 6). 
Localities —Off the east coast of the South Island, between Otago 
Heads and Oamaru ; depths, from 18-44 fathoms. It is confined to 
New Zealand, and apparently to the east coast and Cook Strait. [Far- 
quhar has also noted it from Tasman Bay, Hawke’s Bay, Cape Fare- 
well; and specimens from Stewart Island are in the O.U. Museum. ] 
Variability. 
It is somewhat variable in shape, owing to the greater or less amount 
of interbrachial excavation, so that the relative diameter of ray and 
disc varies; some individuals, also, are much flatter than others. 
The variations affect the following structures :— 
(a.) The proportion of R. to r. (7.e., of the length of the arm or 
ray to the length of the interbrachial region of the disc) is + 2:1. 
In dried specimens it is usually less than 2; in alcoholic specimens: 
more than 2. In a series of five dried ones the lowest proportion is 
R.:r.—1:7:1, and ‘the highest is 2°06: 1. In alcoholic specimens, 
of which four were measured, the lowest is R.:r. = 2:1, and the 
highest is 2°29:1. This comparison also indicates that, in drying, 
the arms shrink more than do the interbrachial areas, which is the. 
