HELIOMETRINAE 137 



about as long as broad. The fourth is longer than broad ; the fifth is nearly, the sixth 

 more than, twice as long as broad. The seventh and eighth are about three times as long 

 as broad. The ninth to about the fourteenth are the longest: more than three times as 

 long as broad. ^ Beyond the fourteenth the segments gradually decrease in length but 

 the most distal are nearly twice as long as broad. They have a less well-marked projec- 

 tion on the dorsal side than those of cirrus a^. The whole cirrus is less robust; it is 

 slightly compressed from side to side. 



The shortest apical cirrus from the same specimen, ^4 , is of 26 segments and about 

 30 mm. long. The first two segments are broader than long, the third nearly twice as 

 long as broad. The fourth is 2\ times as long as broad ; the fifth and sixth are the longest : 

 nearly three times as long as broad. The segments beyond gradually decrease in length 

 to the end, the most distal being, however, nearly twice as long as broad. The segments 

 of this cirrus, particularly the outer and especially on the dorsal side, overlap one 

 another much more strongly than do those of the long cirrus from the same specimen. 



The terminal claw is mostly curved, claw-like and hyaline and there is usually a small 

 opposing spine or the trace of one ; but some of the longer cirri of younger specimens, 

 or even all the cirri of older specimens, may entirely lack the opposing spine, and at the 

 same time the terminal claw may be straight, not claw-like, and it may not be hyaline. 

 The opposing spine may, however, be strong, especially on small apical cirri (Fig. i b). 



The radials, primibrachs and first and second brachials are very variable in shape 

 (Fig. 2 a). They differ, though not constantly nor in the same way, in different speci- 

 mens, with age. Since very few preserved specimens have complete arms it is not 

 possible to use arm length as a rough criterion of age. I have used instead the number of 

 segments in the longer peripheral cirri : in Fig. 2 a the number beside each separate 

 drawing is that of the segments in the longest peripheral cirrus of that specimen. In 

 very young specimens in which the interradial rays are still smaller than the others the 

 alternate radials are of a diff'erent shape and size (flj): those of the radial ray are com- 

 paratively wide, wider at the base than distally; the interradial radials are longer, 

 narrower plates, wider distally than at the base. The distinction in size between the 

 alternate rays does not appear to last long. In older, but still small immature specimens, 

 the radials and succeeding ossicles are of the shapes shown in a.^ or of similar shapes. 

 The radial is long; the costals are not in opposition laterally. The axillary is shield- 

 shaped, longer than broad ; it makes no shoulder-like projection by its incision of the 

 costal. In older specimens the radials are always shorter, and in large specimens they 

 may be very short (Fig. 2, a^ and ^4). In some, but by no means all, old specimens in 

 which the radials are very short the costals are in partial lateral opposition, as if they had 

 been brought down against one another by the reduction of the radials {a^). The axillary 

 may be of any of the shapes shown in Fig. 2 ai-a^ , or of a shape intermediate between 

 them. It may be elongated and longer than broad, or it may be broader than long ; the 

 second brachials vary with it. In the biggest specimens its incision of the costal and the 

 incision of the first brachial by the second make shoulder-like projections which may 

 ^ I have seen these segments four times as long as broad in the cirri of another specimen. 



