ARCTIC SEA TO THE WEST OF GREENLAND. 35 



the inner third, and taper considerably towards the extremity. The disk is small, its 

 radius being proportional to an arm-radius as 1 : 5 '5, or rather less. The ambulacral 

 pores are well spaced, and form two simple rows of sucker-feet. Each adambulacral 

 plate bears two very slender spines, one radiating towards the furrow and the other 

 towards the margin, forming two regular rows of so-called " ambulacral " spines. The 

 spines upon the sides of the arms are much shorter than the ambulacral spines, and com- 

 paratively more robust, being of the same size and character as the spinelets of the 

 dorsal surface. The abactinal network is arranged more quadrilaterally than in Asterctr 

 canthion, a regular median line of ossicles passing down each ray, to which the other 

 ossicles run parallel and transverse, with more or less regularity. A single spinelet is 

 borne at each decussation, and an occasional one frequently on the intercalary ossicle. 

 The spinelets are consequently widely spaced, and assume (although somewhat irregu- 

 larly) a fairly rectilineal arrangement. These dorsal spinelets, which are all of the same 

 shape and structure, resemble those of Stichaster albulus. They are deeply grooved, 

 being formed, in fact, of three or more longitudinal lamellae, which radiate from a 

 common median axis. The extremity of the shaft becomes slightly expanded and trun- 

 cate, and delicate denticles, developed from the free angles of the lamellae, are present 

 at the tip to the number of 3-5. In the ambulacral spinelets the outer margins of the 

 lamellse are serrate or denticulate, whereby, in these appendages, a thorny appearance 

 is imparted to the shaft as well as to the tip. 



The pedicellariae are remarkably large and numerous, and thoroughly characteristic 

 of the genus both in structure and position. One kind only is present, viz. the pedicellariae 

 forcipiformes, which are of extraordinary size, and but very little shorter than the 

 dorsal spinelets ; they stand isolated and alone upon the membranous tissue that covers 

 the interspaces of the abactinal network, about three or four being present in each mesh. 

 No traces of papulae have been detected in the membrane of the dorsal interspaces of 

 the examples under notice. The pedicellariae increase in size in the neighbourhood of 

 the ventral portion of the ray, the length of the calcareous skeleton of many of them 

 measuring 0-35-0-375 of a millim.* The contour of the jaws of the pedicellarise is con- 

 siderably swollen out about the upper third, and then tapers rapidly towards the extre- 

 mity, which is somewhat truncate. Several large curved denticles, usually three or 

 four, occur upon the median portion of the inner margins. The tail-parts of the jaw- 

 pieces are moderately long, and taper towards the extremity ; and, when the pedicellaria 

 is examined from above, the interlocking lips of the jaws are seen to be broad, rounded, 

 and finely denticulate. Every appendage of the body, pedicellariae and spinelets alike, 

 is invested with a thick, semitransparent, cuticular membrane, to which is due the papil- 

 late appearance observable in specimens of the Starfish that are preserved in spirit. The 

 spines are somewhat more crowded upon the disk than upon the rays ; and the " eye "- 

 spines at the extremities form a robust terminal fringe. The madreporiform plate, 

 which is obscure and situated near the margin, bears only two or three striae. 



* The pedicellarise on a young Asteracanthion glacialis, three or four times as large as the present speci- 

 men, do not measure more than O19-O22 of a millim. 



F2 



