yg4 BULLETIN 82, irNrrED STATES NATIONAL MUSEUM VOLDJJB 1 



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

 in<^ slightly longer than the first, the tliird 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 vnth everted and prominent ends. P2 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 P2 bears a gonad. P3 is 8 mm. long, with 20 to 23 

 se'inents, 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. P4 is 8 mm. long, similar to P3 but with a larger gonad and relatively more 

 elongate segments. Pa resembles P4, but has more elongate segments. Large well- 

 rounded gonads are borne by P3, P4, P5, and Pa and the corresponding pinnules on the 

 other side of the arm. These genital pinnules are slightlj'- stouter than the preceding 

 pinnules, especially in the basal portion bearing the gonad. The distal pinmdes 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 Heliometra 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 raj' 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 ccntrodorsal to the middle of the eighteenth 



brachial is 12 mm. 



The ccntrodorsal is hemispherical with about a dozen cirrus sockets irregularly 



scattered over the surface. 



