NOTOCRINIDAE 197 



The arms of the longest specimens are composed of about 114 brachials. The first 

 brachial is slightly incised by and much shorter than the second (Fig. 20 c). The two 

 beyond the first syzygial pair, the fifth and sixth, are almost rectangular and, more 

 especially in the larger specimens, broader than long. Those beyond, to the third 

 syzygy, are wedge-shaped, almost triangular, and nearly as long as broad. The distal 

 become less triangular and more quadrate and, towards the end of the arm, as long as 

 or longer than broad (Fig. 20 d). Towards the end the arm has a zigzag shape because 

 each brachial bends to the side from which its pinnule springs (Fig. 20 e). 



The oral pinnules (Fig. 20 c) are short and stout and taper to blunt ends. They are 

 composed of a small number of rounded segments each of which, except perhaps for the 

 first, is slightly longer than broad. Pj is always heavier and slightly longer than P., and 

 P3, which are of the same length. In the younger specimens Pj is of 8-10 segments, 

 5-5-7 mm. long; Pj and P3 are of 7-10 segments, 5-6 mm. long. In the old specimen 

 from St. 1948 Pj is of 13 segments and 11 mm. long, P2 and P3 are of 12 segments and 

 9 mm. long. P4 is usually an oral pinnule and variable even on the different arms of a 

 single individual: it is of 7-12 segments, sometimes of the same length as, most often 

 longer than, P2 and P3 . It is sometimes a genital pinnule of more segments and greater 

 length. 



Pj is not entirely free : its first two to four segments are directly attached to the disk 

 and one or two beyond are connected with the disk by a web of tissue. The first segments 

 of the other oral pinnules are similarly attached to the arms by webs of tissue. 



The number of genital pinnules on one side of the arm varies in the nine younger 

 specimens from eight to nineteen and is twenty-three in the older specimen. The gonads 

 lie at their bases as in A^. virilis (see below). The first genital pinnules are longer than 

 the orals and they gradually increase in length. The most distal genital and the first of 

 the outer pinnules are the longest ; those beyond decrease in length to the tip of the 

 arm. P5 is usually the first genital pinnule; it is of 11 segments and about 8 mm. long 

 in the younger specimens, of 17 segments and 12 mm. long in the old specimen. The 

 distal genitals are of 17-22 segments, 12-14 mm. long. The pinnules at the tips of the 

 arms may be of only 9 or 10 segments, about 10 mm. long. 



The genital and outer pinnules are composed of round segments the first one or two 

 of which are as long as broad, the others slightly longer than broad. Their distal edges 

 may be produced into a row of fine spines. The ends of the pinnules are often strongly 

 curved. The dorsal sides of the last three or four segments are arched. 



The disk is incompletely plated. There is a close pavement of thin plates completely 

 or almost completely covering the space between the bases of the arm pairs of the 

 younger specimens: in the older specimen the plates are few and isolated; there are 

 usually no plates on the small part of the disk to be seen between the two arms of one 

 pair. On the ventral side of the disk of the younger specimens the plates are fewer and 

 larger. There are one or two large plates at the oral corners of each interradius and rows 

 of large plates along the ambulacral grooves. The anal cone is covered with small plates. 

 The ventral side of the disk of the older specimen cannot be seen. 



