784 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



In less developed individuals the first 2 segments are broader than long, the second be- 

 ing slightly longer than the first, the third is about as long as broad, and the remainder 

 are nearly or quite twice as long as broad; the segments are slightly constricted cen- 

 trally with everted and prominent ends. P 2 is from 5.5 to 7 mm. long with 18 to 25 

 segments, similar to PI but longer and proportionately stouter, with relatively slightly 

 longer segments. In a few cases P 2 bears a gonad. P 3 is 8 mm. long, with 20 to 23 

 segments, which become as long as broad on the third, twice as long as broad on the 

 fifth, and much elongated distally. There is a large gonad on the third to sixth 

 segments. P 4 is 8 mm. long, similar to P 3 but with a larger gonad and relatively more 

 elongate segments. P 5 resembles P 4 , but has more elongate segments. Large well- 

 rounded gonads are borne by P 3 , P 4 , P 6 , and P 6 and the corresponding pinnules on the 

 other side of the arm. These genital pinnules are slightly stouter than the preceding 

 pinnules, especially in the basal portion bearing the gonad. The distal pinnules are 

 extremely slender, with the first segment short and bandlike, more or less crescentic, 

 the second irregularly quadrate, about as long as broad, and the following excessively 

 elongated with somewhat swollen articulations. 



In small specimens the segments of P,, except the basal, are considerably elongated. 



The general relationship between the lower pinnules of this species, and indeed 

 of all the species of this genus, are much the same as those between the lower pinnules 

 in Heliomeira glacialis, though the relative length is reversed. 



The disk typically shows 5 large primary groove trunks given off from the mouth; 

 about half way to the arm bases each of these divides into 2, so that the disk presents 

 the same appearance as that of an ordinary 5-rayed and 10-armed endocyclic form. 

 In most of the individuals, however, one or two of the ambulacra run undivided to 

 the arms, while a corresponding number of the others divide into 3 instead of into 2 

 parts at the arm bases. 



Notes. Many of the specimens show an inequality in the size of the arms, there 

 being one or more considerably smaller than the others. These smaller arms alternate 

 with arms of full size and represent not yet perfected secondary arms derived from the 

 interradials. 



Aberrant specimens. Two of the 40 individuals examined have 9 instead of 10 

 arms, just as in the only known example of T. rugosus; but these are not in any 

 other way different from the remainder. 



Another specimen has only 8 arms, the anterior arm of the left anterior ray and 

 the posterior arm of the right anterior ray being represented by interradial plates 

 which are about half as broad as the adjacent radials, swollen and strongly convex, 

 with the distal border (corresponding to the usual articular face) swollen and rounded 

 off, so that they appear like the ends of two large basal rays shoved from their normal 

 position up into the radial circlet. 



Young. A very interesting specimen from Ingolf station 97 is without doubt the 

 young of this species. It is in almost every detail identical with the young of T. 

 renovatus. 



The total length from the tip of the centrodorsal to the middle of the eighteenth 

 brachial is 12 mm, 



The centrodorsal is hemispherical with about a dozen cirrus sockets irregularly 

 scattered over the surface. 



