ARCTIC SEA TO THE WEST OF GREENLAND. 21 



The following are the measurements in millims. of 



A, a specimen from Discovery Bay ; 



B, a specimen from the Drobach Fjord. 



Interamb. tubercles. 



17 

 15 



Variations. Owing to the extensive range of this boreal Echinoid, the variations 

 to which it is subject are so great that there are perhaps few other species which 

 include in their list of synonyma so large a number of specific determinations. This 

 arises from the fact that distant observers, depending too confidently upon the stability 

 of " local forms," have founded upon these characters numerous so-called new species, 

 all of which, however, have hitherto proved untenable when comparison has come to 

 be made with a large series of specimens. 



Thus a range of examples of the northern varieties, known as S. granulatus (Say), 

 Gould, and S. chlorocentrotus, Brandt, fail to present any characters of sufficient 

 importance to warrant their separation from the drobachiensis group, although, when 

 isolated and extreme examples are compared, the differences at first sight appear very 

 marked. 



When compared with what may be called a typical specimen, the test of the 

 Arctic forms of S. drobachiensis is relatively high, with the contour slightly more arched, 

 and having a larger actinostome and apical disk. The greatest superficial difference, 

 however, is presented by the spinulation. In some forms the spines of the abactinal 

 surface are so small and delicate, and so widely spaced, that the Echinus has almost a 

 naked appearance when placed beside others which are more uniformly clothed ; and it 

 will hardly be necessary to add that a corresponding modification exists in the size and 

 uniformity of the tubercles upon which the spines are borne. The more densely-spined 

 and more uniformly tuberculated urchin represents well the form known as granulating ; 

 and a glance at two such extreme individuals as those just indicated will easily account 

 for much of the confusion which has arisen in this species. 



Both of these forms (the uniformly and the sparsely spined) occur together at 

 several stations in Smith Sound, and extend even to Discovery Bay. At present we 

 are unable to offer any definite explanation of the difference : possibly the variation 

 may be due to stunted growth ; or perhaps it may indicate a sexual character. 



Distribution. 



a. Northward up Smith Sound : Discovery Bay, lat. 81 41' N., 15-20 fms., muddy 

 bottom (Nares's Exped.}, the most northern locality on record ; Richardson Bay, 70 fms. ; 

 Franklin-Pierce Bay, 13-15 fms., stony, bottom temperature 29' 5 Fahr. ; Cape 

 Napoleon ; Hayes Point, 35 fms., bottom temperature 29'5 Fahr. Greenland. 



b. North of American Continent : Assistance Bay (Penny's Exped.). All the east 



