244 
serially as normal in this form (these spines have been somewhat 
damaged in the specimen). The interambulacral space is otherwise 
covered by spines surrounded by pedicellariæ, as on the aboral side. 
Seen from the aboral side this arm is twice as broad as the other 
arms; otherwise there is no indication of its being composed of 
two rays. — With regard to the inner anatomy of this double arm 
it may be noticed that there are only two coeca and two genital 
organs. The two coeca, however, both proceed from the right half 
of the arm, but soon make a little bending so as to occupy each 
one side of the cavity of the composed arm; in the other half of 
the arm the stomach is somewhat swollen, protruding as a rounded 
lobe into the cavity, but there is no indication of a secondary pair 
of coeca heres — It may be remarked that this species is normally 
5-rayed. 
I may recall here the remarkable monstrosities of another 
Asterid from Greenland, Stichaster albulus Stimp., which I described 
in the Report on the Echinoderms of the Danmark-Exzpedition"). 
One specimen (Fig. 1) has two arms coalesced in about half their 
length — or perhaps it ought to be regarded as an abnormal 
division of an arm; other specimens (Figs. 4, 6) "show a curious 
crowding of the regenerating arms, some of them being pushed 
down on the oral side, turning their ambulacral furrow against the 
ambulacral furrow of the larger arms and their dorsal side down- 
wards, the result being a most curious irregularity.” 
In Pl. IV. Fig. 3 is represented a specimen of Astropecten irre- 
gularis (Penn.) with one arm, nr. 2 to the right of the madreporite, 
bifurcating. There is nothing exceptional to observe in the secondary 
arm, the inner anatomy shows, as might be expected, one coecum 
continuing into each branch. This specimen was found at the 
Zoological Station of Kristineberg, Sweden, near a little island named 
"Smedjan”, in a depth of ca. 10 fathoms, in August 1911. Å 
1) Th. Mortensen. Report on the Echinoderms coll. by the Danmark- 
Expedition at North-East Greenland. Medd. om Grønland. XLV. 1910. 
p. 268. Pl. XIIL. Figs. 1, 8, 4, 6. 
