HO BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



The 10 arms are probably about 100 mm. long. The brachials are triangular, 

 slightly overlapping, the later somewhat compressed laterally. The second brachials 

 and the hypozygals of the first syzygial pairs are flattened on the inner side only. The 

 line of junction between the first two brachials is somwehat tubercular. 



Syzygies occur between brachials 3 + 4, again at about the thirteenth brachial, 

 and distally at intervals of from 5 to 16 muscular articulations. 



P, is large and stout; the first eight segments have broad and flattened outer sides, 

 and the third, fourth, and fifth have the inner edges bent upward and somewhat thick- 

 ened, but in the next following these are sharpened and form a keel. P a is similar but 

 smaller, with the outer side flattened. The pinnules of the next two pairs have broad 

 and carinate lower segments, and the later pinnules are more styliform with the two 

 basal segments expanded and trapezoidal and those following elongated. 



The disk is 11 mm. in diameter, thickly covered with plates which extend out onto 

 the arms at the sides of the ambulacra, and also over the gonads. The pinnule ambulacra 

 have well-defined side- and covering-plates. Sacculi are very rare. 



Notes. — The preceding description is adapted from that of Carpenter, with a few 

 additions from his figures. In 1910 I examined two of Carpenter's specimens in the 

 British Museum. This is a large species, resembling in a general way A. eupedata; 

 the distal edges of the radials and the lateral edges of the IBr series and first two brachials 

 are conspicuously dentate with fine well separated teeth. 



In the specimens from Siboga station 122 the dorsal pole of the centrodorsal is more 

 blunted than in Carpenter's specimens, and is studded with numerous small low tuber- 

 cles. The cirrus sockets are in 10 columns which are interradially in apposition, though 

 well separated in the midradial line. There is usually only a single functional cirrus 

 socket to a column. The more distal obsolete cirrus sockets develop conical tubercles 

 of which the axes are parallel to the dorso ventral axis of the animal. These tubercles 

 are proportionate in size to the size of the cirrus socket they occupy; thus below the 

 functional socket in the columns there is in each radial area a double row of tubercles 

 of diminishing size which continues to the dorsal pole, there merging with the small 

 polar tubercles. 



There are three cirri remaining which are composed of 45 (one) and 61 (two) 

 segments; in the first the transition segment is the ninth, in the two others the eighth, 

 the cirri decrease slightly in diameter to the transition segment, and in lateral view 

 increase in diameter on the short distal segments. The longest cirrus segment (the 

 transition segment) is about twice as long as broad. 



The radials are visible as short and broad, more or less irregular, tubercles between 

 the centrodorsal and the IBr,; one or two tubercles springing from them are visible in 

 the angles of the calyx over the ends of the basal rays, and there may be a smaller 

 tubercle between these and the central tubercle. The central tubercle is indicated in 

 Carpenter's figure but is not clearly shown. 



The ends of the basal rays are visible as small low rhombic tubercles in the inter- 

 radial angles; they are more or less obscured by the tubercles arising from the radials 

 above them and by the cirri beneath. 



The proximal border of the IBr, is turned outward and more or less scalloped; 

 the median third of this border is straight and parallel with the proximal border of the 

 centrodorsal; the lateral thirds slant outward and upward and are slightly concave; 



