No. IX. ECHINODERMATA. 269 



In the ' Oversigt over Gronlands Echinddermer,' ' Dr. 



Liitken records that amongst the specimens of G. papposus 

 which he had examined there occurred only one example of 

 the ten-armed variety, those with twelve arms being the 

 most common. 



All the specimens of this collection are ten-armed, with the 

 exception of one small and very young example having nine. 

 Its greatest diameter is only 18 millims. 



When compared with series of similar size from more tem- 

 perate waters, the polar specimens are characterised by finer 

 arms, fewer spine-clusters (bearing fewer but very much 

 longer spinelets), the spine-clusters more widely separated 

 from one another, and the ventral spaces almost naked. 

 These points are so striking in some individuals that at first 

 sight one is tempted to consider that we have here a well- 

 marked variety of this almost cosmopolitan starfish. Careful 

 study, however, of the series leads us to the conclusion that 

 no sound distinction can be drawn ; and we would offer as a sug- 

 gestion explanatory of the divergence, that in these Arctic 

 forms of Crossaster premature phases are more slowly passed 

 through, and that development of detail takes place in a dif- 

 ferent ratio to the body-growth from that which obtains 

 under more favourable conditions of life. 



The largest specimen obtained measures 93 millims. in 

 diameter. 



Brandt founded a species, Asterias affinis, upon a single 

 specimen obtained in Behring Straits, but which, from the 

 short description given, appears only to have been similar to 

 the specimens before us ; and, such being the case, the grounds 

 are not sufficient to warrant the maintenance of his species. 

 In all probability A. alboverrucosa, Brandt, is also identical. 



A singular instance of the rapacity of this starfish may be 

 here related. The disk of one of the large individuals from 

 Discovery Bay being considerably distended, it was cut 

 open; and the distention was found to result from the 

 creature having gorged a young Strongylocentrotus clrdbachi- 

 1 i Vidensk. Meddelelser ' for 1857, p. 40. 



