696 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Description.— Tha centrodorsal is flattened hemispherical with a broad bare dorsal 

 pole equal in width to about one third of the total diameter. The 45 to 60 cirrus sockets 

 are closely crowded around the sides. The peripheral ones are distinctly larger than 

 the apical. 



The cirri are XLV-LX; a complete middle one has 12 segments and is 8 mm. 

 long (fig. 44c). The first segment is from half again to twice as broad as long; the 

 second is nearly twice as long as broad; the third and fourth are nearly three times as 

 long as the median width, slightly constricted centrally; and those following slowly 

 decrease in length so that the antepenultimate is not quite twice as long as broad, 

 at the same time losing the median constriction so that they appear slightly broader 

 in lateral view. The penultimate segment is half again as long as broad. The opposing 

 spine is small, terminal, and directed obliquely forward; its dorsal profile makes prac- 

 tically a straight line with that of the penultimate segment. The terminal claw is 

 about as long as the penultimate segment, rather stout at the base, evenly tapering, 

 and evenly and strongly curved. Judging from the stouter basal segments, the periph- 

 eral cirri were somewhat larger. 



The distal edges of the radials are even with the rim of the centrodorsal. The 

 IBr, arc extremely short, about six times as broad as long in the median line, just in 

 contact basally, with the lateral edges very strongly convergent. The IBr2 (a.xillaries) 

 are triangular, broader than long, the anterior angle, which is not produced, appro.xi- 

 mately a right angle, the anterior sides only slightly concave, the lateral angles ex- 

 tending far beyond the anterolateral angles of the IBr,, yet widely separated from those 

 of the adjacent axillaries, and with a slight well-rounded process in the median 

 portion of the proximal border. 



The 10 arms are from 55 to 75 mm. in length. The first brachials are very short, 

 twice as long exteriorly as interiorly, with the proximal half of the inner edges of those 

 of each arm pair in contact and the distal halves diverging at first in a straight line 

 which later turns abruptly upward in a slightly rounded right angle. Thej^second 



Figure 44. — Retiometra alascana A. H. Clark, holotype: a, Laterodorsal view of calyx; b, base 

 of peripheral cirrus; c, detached, probably middle, cirrus; d, Pj (incomplete); e, Pz. 



