350 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



minnl segments. P„ is similar but rather smaller. P 2 has fewer segments, but the 

 third and fourth are relatively broader, and in the succeeding pinnules very much 

 broader with their outer faces greatly expanded toward the ventral side. This condi- 

 tion is most marked at about P 6 and then gradually decreases, being traceable to Pi 2 

 or P :5 . After this is lost the pinnules gradually diminish in stoutness, but do not 

 increase much in length. 



The disk is 7 mm. in diameter and is much incised and completely plated, as are 

 also the arms both along the ambulacra and at their sides. The gonads are protected 

 by stout anambulacral plates. The ambulacra of the distal pinnules have well defined 

 side plates alternating with, but often partly concealing, the sacculi, which are abun- 

 dant and very large, especially on the genital pinnules. 



The color in alcohol is dark gray-brown, of the young individuals yellowish brown. 



Notes. — In the Challenger report on the stalked crinoids Carpenter noted that in 

 this species the irregular double row of transversely oblong plates bordering the am- 

 bulacral grooves on the disk is barely distinguishable from the anambulacral plates, 

 and the whole set encroaches very much upon the peristome so that in a dry state it 

 is scarcely visible. 



He said that the first pair of pinnules in this species are considerably different 

 from their successors. Pi is rather larger than P ft , but the general characters are 

 identical. All the segments are quite short, but the first five or six are broad, carinate, 

 and trihedral, with their outer sides flattened somewhat as in Aglaometra valida and 

 allied species. Traces of this flattening are apparent on P 2 , but P b and the following 

 pinnules have the third and fourth segments very broad and expanded, though the 

 fifth is smaller again and its successors very much so. These lower segments, which 

 are so broad and almost flat on their outer side, afford support and protection to the 

 gonads which are situated on their inner faces. The ventral surface of the gonads is 

 covered by a pavement of anambulacral plates often with large sacculi imbedded in 

 them here and there. But there are no side and covering plates as in the distal pin- 

 nules. Carpenter said that the expansion of the third and fourth pinnule segments is 

 best developed about the tenth or twelfth brachials, after which it gradually becomes 

 less and less marked and the later segments more and more elongated. But the third 

 and fourth segments are often distinctly broader and flatter than their successors as 

 far out as the thirtieth brachial, after which they assume a more elongate form. 



Carpenter said that in one quite young specimen about one-third the size of a 

 fully grown individual there is comparatively little trace of the expansion of the third 

 and fourth segments even on the lower pinnules. The arms, too, are much smoother 

 than in the adult, the edges of the lower brachials being but slightly raised and showing 

 no trace of the crenulation which is so marked in the more mature individuals. The 

 radials are just visible as narrow curved bands immediately above the centrodorsal 

 which are not smooth and continuous as usual but broken here and there by pits. In a 

 slightly older individual they are represented only by a row of irregular processes 

 between the centrodorsal and the IBri, while in the mature form they are altogether 

 invisible, though traces of the processes appear after the removal of the IBr,. 



In this species Carpenter noted that the upper surface of the centrodorsal is so much 

 larger than the base of the radial pentagon that the IBri partly rest upon it and so 

 completely conceal the radials as in some forms of Antedon bifida. The cirrus sockets 



