28 ON THE ECHINODERMATA OF THE 



the Starfish ; and, further, in some examples the disk-spinelets are also rather longer 

 than those which are found upon the rays. 



The papulae are single. The pedicellariae are not crowded, and generally either 

 isolated or only two or three together. Pedicellarise forcipiformes are as a rule not 

 very numerous upon the dorsal surface of the rays, except towards the extremities, where 

 they occur somewhat more abundantly. Those which accompany the lateral spines are 

 situate near the middle of the shaft. Pedicellariee forficiformes form a fringe along 

 the sides of the ambulacral furrow. The madreporiform body is situated near the 

 margin, and is frequently almost concealed by the spinelets that surround it. 



Size. This comparatively small species measures from 35 to 50 millims. in diameter, 

 none of larger size having been recorded. 



Colour. According to Inspector Olrik's observations, made during life, small 

 examples of A. grcenlandicum are described as of a greyish colour on a violet ground, and 

 larger ones of a grey olive-green. All the specimens preserved in spirit which we have 

 examined are entirely bleached, whilst the dried ones are of a dirty yellowish grey. 



Habitat. Mr. Barrett has taken this Starfish upon rocks near the shore ; Insp. Olrik 

 reports that he has dredged it at very various depths ; and Capt. Feilden obtained the 

 species from a depth of 80 fathoms, off" Cape Frazer, during the British Arctic Expedi- 

 tion of 1875-76, under Capt. Sir George Nares. 



Variations. In this species considerable variation occurs in the general form and 

 habit of the Starfish, as well as in the spinulation borne by the calcareous network of 

 the test. There may, in fact, be set apart a long, thin-armed variety with the rays taper- 

 ing but slightly, and another form in which the rays are broad, short, and sharply 

 tapering at the extremity. The difference of character presented by the spinulation is 

 perhaps even more conspicuous. In some specimens, for example, the spinelets of the 

 abactinal surface of the rays are confined mainly to the groups that stand at the intersec- 

 tions of the network, the intermediate portions of the ossicles bearing only isolated spine- 

 lets, few and far between ; whilst in others a very marked divergence is produced by 

 the occurrence of well-developed and comparatively clustered groups of spinelets upon 

 the intercalary pieces, as well as an increase in the number of those composing the main 

 series. The effect of this tendency to develop an increased number of spines is perhaps 

 most striking in its result on the lateral series, where, in consequence of the intercala- 

 ting ossicle bearing a supplementary spinelet, an additional and intermediate longitudinal 

 series is formed between the dorsal and ventral rows of lateral spines, extending in some 

 cases almost to the extremity of the ray ; and besides this, it not unfrequently happens 

 that the development of extra spines is carried to such an extent that a regular redu- 

 plication of several of the lateral spinelets at the base of the rays takes place. 



It must be remarked, however, that, beyond the simple record of the facts, the 

 amount of material at our disposal is insufficient to warrant the expression of any decided 

 opinion as to the significance which these modifications may bear ; for, although at first 

 sight it would seem probable that these were only the conditions of age and growth, a 

 careful study of the specimens which we have examined, together with the consideration 

 of the influence of habitat, lead us to favour the belief that the structural changes above 



