268 



Th. Mortensen. 



Nanaster {Stichaster) albulus Koehler. 1909. Échinodermes. Monaco. 



XXXIV. p. 107. 



Several specimens from Stations: 16, 21, 25, 27, 36, 48, 49, 50, 

 53, 56, 57, 58, 60, 61, 63, 69, 71, 72. ^ 



There are several large specimens among them, the largest 

 having R == 33 mm. These are almost all 7-armed, only one of 

 these large specimens is 6-armed. The arms are all fully developed 

 and nearly of the same length (PI. XIII. Figs. 2, 5); it seems evident that 

 these specimens are fullgrown and have ceased the self-division. — 



Some of the younger 

 specimens show a cu- 

 rious crowding of the 

 regenerating arms, some 

 of them being pushed 

 down on the oral side, 

 turning their ambula- 

 cral furrow against the 

 ambulacral furrow of 

 the larger arms and 

 their dorsal side down- 

 wards, the result being 

 a most curious irregu- 

 larity (PI. XIII. Figs. 4, 

 6). In a specimen from 

 Stat. 58 two of the lar- 

 ger arms are coalesced 



Fig. 3. Stichaster albiilus. Nat. size. nearly in their 1ппеГ 



half length, the ambu- 

 lacral furrows remaining separate (PI. XIII. Fig. 1); another specimen 

 from the same station shows a similar concrescence, but to a smaller 

 extent. In a specimen from Stat. 60 the curious feature is seen that, 

 besides the usual reproduced half part, a pair of young arms are 

 growing out between two of the large arms (PI. XIII. Fig. 3). 



The text-figure 3 represents some difïerent division-stages of this 

 curious species. The figure was made for a popular account on the 

 Fauna of Greenland, but I have thought it well worth repro- 

 ducing here. 



The dorsal spines (PI. XIV. Fig. 8) end in 3—4 erect thorns, 

 as correctly described by Duncan & SI ad en. The adambulacral 

 spines are somewhat longer and coarser, but likewise thorny only at 



^ The localities of the different stations are given below, p. 300. 



