446 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



P 2 , with the same number of segments, but somewhat stouter. The following pinnules 

 gradually increase in length and in the number of their component segments, the 

 segments in the terminal portion becoming proportionately more elongated. PIO is 

 9 mm. long and the distal pinnules are 12 mm. long with 15-17 segments of which 

 the first is about twice as broad as long, the second is about as long as broad, the third 

 is about one-third again as long as broad, and those following increase very gradually 

 in length, being distally about three times as long as broad. The color in alcohol is 

 brownish white. 



Additional details were given in 1909. The first brachials are wedge-shaped, 

 rather longer outwardly than inwardly, inwardly united for their entire length. The 

 second brachials are similar in shape and size but are united interiorly. The first 

 syzygial pair (composed of brachials 3+4) is oblong, about twice as broad as long. 

 The next two brachials are oblong, about three times as broad as long, those follow- 

 ing becoming wedge-shaped, and triangular about half again as broad as long after 

 the tenth. The terminal four to six brachials are very short and abruptly incurved, 

 the terminal pinnules reaching about 4 mm. beyond them as in the other species of 

 the genus. The IBr series and the first 9 or 10 brachials are in close apposition and 

 sharply flattened laterally. The arms in the proximal half are rounded dorsally, 

 but after the middle gradually become compressed and strongly carinate, the brachials 

 developing strong overlapping spines. Syzygies occur between brachials 3+4, again 

 from between bracliials 5 + 6 to between brachials 13 + 14 (usually between brachials 

 12+13 or 13 + 14, with sometimes an extra one between brachials 7+8) and distally 

 at intervals of 4-7 (usually 5 or 6) muscular articulations. 



I wrote that the most obvious distinguishing characters of this species are the 

 small rounded-conical centrodorsal bearing comparatively small cirrus sockets and 

 the smoothness and slenderness of the lower part of the animal. From the base of 

 the centrodorsal the increase in width is gradual and regular, reaching a maximum 

 at about the level of the first syzygy. In A. macropoda and in A. anthus, I said, 

 the cirrus sockets are much larger, the centrodorsal is columnar for most of its length, 

 and the diameter of the animal increases rapidly to the distal end of the IBr! but 

 more gradually from then on so that the opposite sides of the animal are more 

 nearly parallel. This gives these species a peculiarly robust appearance in contrast 

 to the more slender A. lepida. While the basal portion of A. longidrra increases 

 uniformly in thickness, the increase is much more rapid than in A. lepida; A. longidrra 

 is a considerably stouter and more robust species with a larger centrodorsal, and the 

 IBr series are sharply tubercular, a character quite absent in A. lepida. The mus- 

 cular fossae on the articular faces of the radials in A. lepida resemble those of A. 

 macropoda. 



The 14 specimens from Mortensen's station 9 according to Gislen present the 

 following features. (1) The cirri are XIII, 60-71, 37-54 mm. long; the 10 arms are 

 57 mm. long; there is no carination of the IBr series; P t is 4.6 mm. long with 10 

 segments; P 2 is 4.8 mm. long with 10 segments; the distal pinnules are 8.2 mm. long 

 with 18 segments. (2) The cirri are XVII, with up to 74 segments, 35-60 mm. long; 

 the 11 arms are 60 mm. long. (3) The arms are 10 in number, all broken. (4) The 

 cirri are XVI, with up to 75 segments, up to 60 mm. long; the 10 arms are 65 mm. 

 long. (5) The cirri have about 75 segments and are 50 mm. long; the 11 arms are 



