Bd. VI: 4) THE ECHINOIDEA. 3 



I beg here to tender my best thanks to Professors Hj. Theel, H. Ludwig, L. 

 Doderlein, L. Joubin, G. Pfeffer, Drs. O. Steinhaus, R. HARTMEYER and the 

 late Dr. M. MEISSNER, who have with the greatest liberality answered my requests 

 for material, loan of type specimens or information on special points. To Mr. H. 

 LYNGE I am indebted for the identification of some bivalve molluscs, commensalistic 

 on some of the Echinoidea in the collection of the South Polar Expedition. 



Fam. Cidaridae. 



Ctenocidaris n. g. 



The test not very high, the vertical diameter ca. 50 — 60 % of the horizontal 

 diameter, not reckoning the generally much elevated anal system. Ambulacra ca. 

 1 5 as wide as the interambulacra; the pores very close together, the partition-wall 

 even generally interrupted. The secondary tubercles very numerous and close, leav- 

 ing no naked median space in either ambulacra or interambulacra. In larger speci- 

 mens there are 8 — 9 interambulacral, ca. 60 ambulacral plates in each series. The 

 apical system ca. 45 % of the horizontal diameter; all oculars excluded from the 

 anal system. The peristome ca. 36 — 40 \ of h. d.: interambulacral plates on the 

 peristome reaching the mouth-edge in larger specimens. The radioles scarcely exceed 

 the h. d. in length, rather closely set with small serially arranged thorns; otherwise 

 covered with anastoming "hairs". The actinal radioles very coarsely serrate. Se- 

 condary spines cylindrical, clubshaped, those around the radioles more or less flat- 

 tened; they are generally rather erect. The pedicellariae are elongate, with a rather 

 small, irregular opening, without end-tooth; only one kind known, probably repre- 

 senting the small globiferous form. Spicules of the usual shape. 

 Hitherto known only from the Antarctic Ocean. 



The relations of this genus must evidently be sought for among such forms as 

 RhyncJiocidaris and Notocidaris. The pores and the secondary spines seem to point 

 in this direction (the special character of the pores in Rhynchocidaris triplopora is 

 not in disagreement herewith). The shape of the actinal radioles is peculiar in each 

 of the three genera. The pedicellarise, unfortunately, cannot be discussed in this con- 

 nection, as the only form known from Ctenocidaris is probably the small globiferous; 

 but it is the large form of globiferous pedicellariae which is the more characteristic 

 and thus the more important of the two forms. In any case the fact that there is 

 no end-tooth on the pedicellariae of Ctenocidaris is in accordance with the suggestion 



