26 ON THE ECHINODEKMATA OF THE 



outwards. The ambulacral spines are stout and cylindrical, two to each ambulacral 

 plate ; and every pair radiating at the same angle, a regular double row is formed on 

 both sides of the furrow. 



Variations. The number of rays is very constant at six, although examples having 

 only five are occasionally met with. 



A considerable amount of variability occurs in the spinulation of the dorsal surface. 

 In some specimens the spinelets are densely grouped, in others well spaced and with 

 the encircling pedicellarise more conspicuously displayed. The spines themselves are 

 either cylindrical, with tips sharply pinched together, or fairly clavate and resembling 

 in character the spinelets of A. violaceum, O. F. Miiller. It would seem that these 

 differences exist irrespective altogether of age or growth. 



Similarly variable in character appears the arrangement of the ambulacral spinelets, 

 as indicated by the deviation from the regular double row on either side the furrow to 

 the fourfold series produced by the greater divergence of the alternating pairs. In fact, 

 we are disposed to believe that the two modes of arrangement may be present on a single 

 individual, and that it was probably such a specimen that M. Perrier referred with doubt 

 to the species under notice, giving at the same time a most admirable and lucid 

 description, which leaves no doubt as to the correctness of his determination*. 



It may be inferred, from the description given in the ' Fauna Grcenlandica,' that 

 A. polare and possibly also A. grcenlandicum were merged together by Fabricius under 

 the designation of Asterias rubens ; and it also seems highly probable that the Starfish 

 there named A. minuta is nothing more than a young stage of the present species an 

 opinion which Dr. Lu'tken has already expressed f. 



The description given by Brandt of A. ochotense, in MiddendorfFs ' Reise '$, indicates 

 a range of variation which leads to the assumption that more than one form may be 

 there included. If such a view be correct, a part of the description there given would 

 answer well for young forms of A. polare. 



Miiller and Troschel's type specimens of this species were also unquestionably 

 young examples. 



Distribution. 



a. Greenland : W. coast of Davis Strait, about lat. 70 N. (Sabine) ; Upper Torske 

 Bank, lat. 67 50' N., long. 55 27' W. ('Valorous' Exped.) ; lat. 66 59' N., long. 

 55 27' W., 57 fms. (' Valorous ' Exped.) ; W. coast of Greenland, lat. 65 N. (Nares's 

 Exped.) ; Arksut, lat. 61 10' N., long 48 15' W. (Barrett). 



b. North of American Continent : Labrador ( Verrill) ; St. George's Bank, 

 35-40 fms. 



d. North of Asiatic Continent : Ochotsk Bay 1 (under the name of A. ochotense, 

 Brandt). 



* Perrier, Recherches sur les Pedicellaires et les Ambulacres des Asteries et des Oursins, 1869, p. 33. 



t Vidensk. Meddel. Naturh. Forening i Kjobenhavn for 1857, p. 29. 



J Middendorffs ' Eeise in den aussersten Nordon und Osten Siberiens,' Bd. ii. Th. 1, p. 28. 



