32 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
»Beim Eierlegen beobachtete ich, dass die winzigen Eier, welche in continuirlichen 
Massen den Genitalporen entströmten, zunächst auf die nackten Interambulacralplatten 
gelangten und dort sich vertheilten. Sie blieben hier auf der Schalenoberfläche an 
der Sculptur der Schalen haften.» Another important observation was made by 
BERNARD (Op. cit.) : »A. Dufresnii est incubateur ; j’ai trouvé sur un exemplaire de 
moyenne taille un jeune Oursin de 6 millimètres logé dans un enfoncement de la 
membrane buccale; les cinq zones ambulacraires étaient enfoncées de même.» A. 
Dufresnii thus appears not to have pelagic larvæ. * (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. 1, 4—5, 7, 11, 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. 
1 1 mm. 
6.8 — 5 mm - 
8 mm. 
19 mm. 
20—21 
15—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 Südpolar-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. 
