4 TH. MORTEN SEN, (Schwed. Siidpolar-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 Ctcnocidaris and these 

 two genera. 



Ctenocidaris speciosa n. sp. 



PI. 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 



25 



14 



20 



69 





51 



31 



5-5 



2 5-5 



61-63 



8-9 



23 (23-51 



13 



•9 



54 



tf 



5 1 



26 



6 



25 



53-54 



8-9 



23 



'3 



20 



58 



9 



46- 



28 



5-5 



24 



ca. 60 



8-9 



(? brol. 



en -) 



18 



60 



9 



43 ** 



22 



5 



22 



ca. 45 



7-8 



19 





>S 



52 



9 



19** 



9 



2 



9 



f 



6-7 



7-5 





8 



4i 





18.5 



8.5 



2 



9 



27-28 



6-7 



8.5 



4.2 



8. 5 



28 





6 



3 



0.8 



3 



II — 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 pedicellarise); 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. 



