74 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



plates, the width of this adoral ridge varying somewhat. The first two to four 

 plates have one spine each. 



The mouth plates resemble those of acervata and each has three spines in similar 



fashion. 



The papulae are numerous in small not very crowded groups of 10, 15, or even 

 more, dorsally, intermarginally, between the inferomarginals and first actinals, and 

 between the first and second where present. The papulae alternate with the spines of 

 the second actinal row, or when this is not present stand, at least in large, specimens, 

 between the first actinals and the adambulacral plates. There is often only one, at 

 most only a few, papulae to each group aetinallv. 



Madreporic body prominent large, slightly convex, with radiating striae. It is 

 situated about at the middle of r. 



Straight pedicellariae are similar to those of acervata and vary in size but are 

 consistently large; only a very few specimens have them of inferior size. They 

 are generally very numerous, and have either smooth or notched edges. 



( n.ssed pedicellariae (pi. 31 , figs. 1-16; pi. 30, fig. 5) are very numerous and vary in 

 full sized specimens from about 0.25 to 0.29 mm. in length, 0.27 mm. being the usual 

 size of the abactinal. The adambulacral spine pedicellariae which have the usual 

 different form are about 0.3 mm. In arctic specimens the general appearance of the 

 pedicellaria is close to that of polaris, and as in forma acervata, the lip extends farther 

 down on the side of jaw than in southern examples. (Compare figs. 1 and 16, pi. 31.) 



Anatomical notes. — The main features of the anatomy are similar to those of 

 acervata. The intestinal and hepatic coeca are similar. The latter are relatively 

 very large, especially in the large specimens and reach to the end of the ray. They 

 fill the coelom of the ray and extend into the shallow lateral pockets of the coelom 

 fori ned by internal partitions. The latter are due to internal dorsal processes of the 

 marginal and actinal plates overlaid by membrane. The gonads of the largest 

 specimens open more in the axils, than on the ventral surface, but this opening is 

 below the superomarginal plates and is distinctly not at all dorsal as in Asterias, ss. 



An examination of the skeleton reveals no important points of difference. The 

 abactinal plates in large specimens are quite irregular and are crowded in the median 

 region, the meshes being smaller than the skeletal intervals. The supramarginal and 

 intermarginal meshes are the largest. The marginal and actinal plates are regularly 

 four-lobed, the dorsal (internal) lobes being the longest and carinate, so as to support 

 a membranous partition, the series of which, along the side of the ray, act as a support 

 and occasion shallow lateral pockets of the coelom. These elongate dorsal lobes are 



si at the base of the ray, and they overlap very broadly the descending lobe of the 

 plate above, the latter being external. In the large specimen from station 3251, 

 there is a third series of small actinal plates which can not be seen from the outside. 

 As mentioned elsewhere the large tubercles are borne on very convex plates much 

 larger than the others. These plates seem to be among the first formed in the young. 



Variations. — The principal variations have been stated in the description. 

 It will be necessary only to give a brief summary here. 



The number of rays is six, but there is one specimen with five rays from station 

 3518. The stoutness of the rays varies independently of the size of the specimen, the 

 condition depending partly on the maturity of the gonads, also somewhat upon the 



