248 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



the third longer than broad, and the fourth about half again as long as broad; the 

 remaining segments are all of about the same proportions; the opposing spine is always 

 prominent, but small, terminal or subterminal in position, directed obliquely forward; 

 the terminal claw is about the length of the penultimate segment, moderately stout 

 and moderately curved. The segments in the proximal two-thirds of the cirri have 

 markedly swollen articulations, this feature dying away distally on the ventral surface 

 of the cirri but persisting to the end on the dorsal surface so that in a lateral view the 

 later segments have a flat or slightly convex ventral profile and a rather strongly con- 

 cave dorsal profile, which in some specimens is so marked as to give the appearance 

 of two dorsal spines, one proximal and one distal, on each segment. The cirri are 

 well rounded in cross section basally, but become somewhat compressed laterally in 

 the distal half. (See fig. 13,e, p. 198.) 



The edge of the radials in the mid-radial line is usually even with the edge of the 

 centrodorsal, but often projects slightly. 



The IBr] are oblong, about twice as broad as long, the sides more or less parallel 

 and furnished with a rounded ventrolateral projection in the distal half (fig. 13,/, p. 

 198). The IBr 2 are rhombic, slightly broader than long, with the distal angle rather 

 low and with the middle of the proximal border raised into a slight broad rounded 

 tubercle in the formation of which the distal border of the IBr, is also involved. 



Ten slender arms up to 110 mm. long; first brachial wedge-shaped, about twice 

 as long outwardly as inwardly, exteriorly provided with a thin flangelike ventrolateral 

 border continuing a similar border on the IBr 2 and the anterior half of the IBr u the two 

 on each ray interiorly united for about half their length, their inner edges forming a 

 right angle with each other beyond their union; the interior anterolateral angles of the 

 first brachials are furnished with a thin rounded projection; second brachials wedge- 

 shaped, longer outwardly than inwardly, somewhat larger than the first; their shape 

 may become more or less irregularly quadrate owing to the greater or lesser develop- 

 ment of a rounded posterior process incising the first brachials, and the central portion 

 of the proximal border usually rises to a more or less evident tubercle with the distal 

 border of those ossicles; third and fourth brachials (forming the first syzygial pair) 

 nearly oblong, but very slightly longer inwardly than outwardly, about half again as 

 broad as long; next four segments wedge-shaped, but with the ends not especially ob- 

 lique, about twice as broad as their median length; ninth and tenth brachials (second 

 syzygial pair) similar, though slightly longer; following brachials more obliquely wedge- 

 shaped, about as long as broad, very gradually becoming more and more elongated 

 with the ends less and less oblique, the terminal ones being about two and a half times 

 as long as broad with somewhat swollen articulations. 



Syzygies occur between brachials 3+4, 9+10, 14 + 15 and distally at intervals of 

 usually three muscular articulations. 



P! is from 8 to 11 mm. long, with 13 to 18 segments; P 2 is from 5.5 to 7 mm. long with 

 10 to 12 segments; P 3 is 5 mm. long with 8 to 11 segments. The pinnules are similar 

 to those of A. bifida, but the denticulation of the distal edges of the segments is not 

 so pronounced and the component segments of the lower are somewhat and of the 

 distal much longer. 



In a specimen from Naples Professor James A. Grieg found well-developed deposits 

 along the ambulacral grooves, consisting of rough, straight or slightly curved, rods 

 alternating with the sacculi and extending from the ambulacral lappets downward 



