4 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
of the relationship of this genus with Rhynchocidaris and Notocidaris. — - To An- 
strocidaris and Eurocidaris the relation is evidently not so very near; the flattened 
secondary spines and very little specialized actinal spines of the two latter genera 
are features which speak against very near relation between Ctenocidaris and these 
two genera. 
Ctenocidaris speciosa n. sp. 
PL I— II, PI. Ill Figs. 1—2, PI. IV Figs. 1—3, PI. XIII. 
Diameter. 
Height. * 
Width of 
Number of Plates. 
Apical 
system. 
Anal 
system. 
Peristome. 
Longest 
Radioles. 
Ambu- 
lacra. 
Interamb. 
Ambu- 
lacra. 
Interamb. 
53 ** 
31 
6 
26 
ca. 60 
8-9 
2 5 
H 
20 
69 
c* 
51 
3 1 
5-5 
2 5-s 
61-63 
8-9 
2 3 ( 2 3 s) 
13 
19 
54 
d 
5 1 
26 
6 
2 5 
53-54 
8-9 
2 3 
13 
20 
58 
9 
46 ** 
28 
5-5 
2 4 
ca. 60 
8-9 
(? brok 
en — ) 
18 
60 
9 
43** 
22 
5 
22 
ca. 45 
7-8 
19 
? 
15 
5 2 
9 
19 ** 
9 
2 
9 
? 
6-7 
7-5 
? 
8 
41 
18.5 
8.5 
2 
9 
27—28 
6-7 
8.5 
4.2 
8.5 
28 
6 
3 
os 
3 
1 1 — 12 
6 
3-2 
1.2 
3 
10 
3-5 
1. 8 
°-5 
2 
6-7 
4-5 
2 
0.6 
2 
4 
The shape of the test is somewhat variable, the height being sometimes only 
half the horizontal diameter, sometimes — and this seems to be the more general 
case in the grown specimens — rather more, up to 62 / of the horizontal diameter, 
as seen from the above measurements. In younger specimens it is generally equal 
to half the h. d. The sides of the test are rounded, the upper and lower sides some- 
what flattened; the border of the peristome is rather strongly incurved. 
The ambulacra are distinctly undulating in the upper part. Inside the primary 
tubercle there is, at the lower edge of the plate, another tubercle of about the same 
size and further one more in the inner corner of the plate, the spaces between these 
tubercles having quite small, miliary tubercles (carrying pedicellariæ); there is thus 
no naked median space left (PI. XIII Fig. 13). The inner of the secondary tubercles 
is developed only at the ambitus, not in the actinal or abactinal part; in younger 
specimens only the outer secondary tubercle is developed, the interporiferous zone 
of the ambulacra thus being covered by 4 series of tubercles, as is also the case 
* In the height is not included the elevated anal system. 
** The specimens thus marked were not denuded; some of the measurements are therefore not fully 
reliable (e. g. the peristome) or even omitted and the number of the ambulacral plates not quite exact. 
