32 TH. MORTENSEN, (Schwed. Siidpolar-Exp. 



»Beim Eierlegen beobachtete ich, dass die winzigen Eier, vvelche in continuirlichen 

 Massen den Genitalporen entstromten, zunachst auf die nackten Interambulacralplatten 

 gelangten und dort sich vertheilten. Sie blieben hier auf der Schalenoberflache an 

 der Sculptur der Schalen haften.» Another important observation was made by 

 Bernard (Op. cit): »A. Dufresnii est incubateur; j'ai trouve sur un exemplaire de 

 moyenne taille un jeune Oursin de 6 millimetres loge dans un enfoncement de la 

 membrane buccale; les cinq zones ambulacraires etaient enfoncees de meme.» A. 

 Dufresnii thus appears not to have pelagic larvae. * (None of the specimens in 

 hand carry young ones on the peristome.) The statement of the occurrence of the 

 species at Nightingale Island thus becomes less probable — and fortunately I am 

 able to prove that it is wrong, resting on incorrect identification. Having received 

 a specimen from Nightingale Island from the British Museum I was at once struck 

 with the considerable difference in the general habitus between this specimen and 

 the specimens from South America, and a careful examination has shown that it is 

 by no means identical with A. Dufresnii. It makes a very distinct new species, 

 which I shall describe and figure here under the name: 



Arbacia crassispina n. sp. 



(PI. V. Figs. 1—3, PI. XV. Figs, i, 4—5, 7, n, 14.) 



Diameter. 



Height. 



Peri- 

 stome. 



Apical 

 system. 



Anal 

 system. 



Width at 



ambitus of 



Number of plates. 



Longest 

 spines. 



ambulacra. 



inter- 

 ambulacra. 



Ambulacra. 



Inter- 

 ambulacra. 



45 mm. 



22 mm. 



24 mm. 



II mm. 



6.8 — 5 mm - 



8 mm. 



19 mm. 



20—21 I5 — 16 



30 mm. 



The shape of the test is somewhat low; the circumference round. On the ab- 

 actinal side the interambulacra are slightly sunken towards the apical system, the 

 ambulacra thus being slightly prominent. 



The ambulacral primary tubercles increase regularly in size from the peristome 

 towards the ambitus; above the ambitus large and small tubercles alternate irregularly. 



* In the list of the Antarctic Echinoids, which are known to be » viviparous* (strictly taken this word 

 is not correct here, where it means only »care of the brood*), given in the Report on the Echinoidea of 

 the German South Polar Expedition (Ergebn. d. deutschen Siidpolar-Exped. IX. Zoologie III. p. 104) 

 A. Dufresnii is not included, as I had forgotten Bernard's observation. Likewise Ludwig appears to have 

 overlooked this observation, this species being not included in the list given in his paper »Brutpflege bei 

 Echinodermen* (Zool. Jahrb. Suppl. VII). 



It would be very desirable to have the observation by Bernard on the viviparous habit of this spe- 

 cies confirmed. It cannot be denied that this occurrence of one young on the peristome is somewhat re- 

 markable in view of the evidently enormous number of eggs. Can it perhaps be that this young one had 

 accidentally got on the peristome during the capture in the dredge or even in the preserved state? In any 

 case it would be very desirable to have the question reexamined. 



