6 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
edge the pores may be more or less irregularly arranged. The inner plates do not 
join those of the neighbouring series, so that the interambulacral plates may proceed 
right to the mouth opening. The inner plates are densely tuberculated along their 
inner edge, the outer ones naked. 
The radioles do not much exceed the h. d. in length, only in one case, in a 
young specimen of 19 mm, I find them a little more than twice as long as the h. d. 
They are slightly tapering towards the point, rather closely set with small thorns, 
which are arranged in longitudinal series, especially in the outer part, less distinctly 
so in the lower part (PL XIII Fig. 1 1). The ostracum is covered by a dense clothing 
of anastomosing hairs, which make a conspicuous meshwork round the radiole (PI. 
XIII Fig. 5). The inner, reticulate portion of the spine is somewhat unusually large. 
Towards the actinostome the radioles, as they become shorter, become gradually 
more coarsely thorny in the lower part and more deeply furrowed in the outer part, 
the point being often a little widened and irregularly cupshaped. Two lateral series 
of thorns soon become much the larger, and the radioles nearest the peristome have 
these coarse lateral serrations alone (PL III Fig. 2, PL XIII Figs. 7, 8, 10, 12, 15). 
These latter radioles are also somewhat curved towards the point. — The milled 
ring is somewhat unusual, not distinctly limited against the lowermost part of the 
radiole, the furrows continuing almost to the edge of the articular cup. 
The secondary spines are very numerous, rather erect. The smaller ones are 
quite cylindrical, more or less clubshaped; the larger ones, those around the radioles, 
are somewhat appressed, a little widened and flattened towards the point; they reach 
a length of ca. 6 mm. The spines of the apical system are short, only those sur- 
rounding the anal opening rather long. The spines of the peristome are somewhat 
flattened, as is usually the case in Cidarids. 
The pedicellariæ are represented — in the available specimens — by one form 
only, which must probably be taken to be the small globiferous form, though it 
reaches a rather large size, ca. 0.8 mm, length of head. The valves (PL XIII Figs. 
4, 14) are very slender and elongate, the side-edges often being somewhat concave. 
The opening is often somewhat irregular, the lower edge being sometimes straight 
across, sometimes somewhat downwards curved, or the opening may even end in a 
small slit below. The side-edges generally continue directly into the edges of the 
opening, but sometimes they are separated therefrom more or less distinctly, though 
never widely. The glandular cavity is narrow, very slightly elevated; generally it 
is smooth, but sometimes some small irregular, serrate projections occur. The stalk 
is without limb. The rather thick skin covering the stalk and head is richly 
provided with brownish chromatophores. — It may seem probable that large globi- 
ferous pedicellariæ will also prove to occur in this form, though certainly not com- 
mon, since they are not found in any of the available specimens. On the other 
