PART 5 A MONOGRAPH OF THE EXISTING CRENOIDS 261 



are relatively long, not more than three times as broad as long, regularly oblong or 

 slightly trapezoidal, the lateral edges usually making a straight line, more rarely a 

 broadly obtuse angle, with those of the axillary. 



Description. The centrodorsal is flattened hemispherical, about 4 mm. in diameter 

 at the base, the bare dorsal pole flat, about 1.5 mm. in diameter; the cirrus sockets are 

 arranged approximately in three closely crowded alternating rows, of which the upper- 

 most includes about four sockets in each radial area. 



The cirri are XXV-XL (usually XXX-XXXV), 22-30 (usually 24-28) 20 to 27 

 mm. in length, long, slender, and of uniform thickness throughout their length; the 

 first segment is very short, the second about half again as broad as long, the third about 

 as long as broad, the fourth half again as long as the width of its expanded ends, the 

 fifth and following about twice as long as the width of the distal ends, the proportions 

 remaining practically the same to the end of the cirrus, though the distal segments 

 may be a trifle shorter than those nearer the base; the penultimate segment is nearly 

 or quite twice as long as broad, with a prominent, slender and sharp opposing spine 

 which is subterminal in position, directed slightly forward or nearly erect, and equal to 

 about half the distal diameter of the penultimate segment in height; the terminal claw 

 is slender, evenly tapering, moderately and uniformly curved, about equal to the penul- 

 timate segment in length. The fourth and following segments are moderately con- 

 stricted centrally, so that the ends are prominent; this feature slowly diminishes in 

 intensity in the distal half of the cirri. The cirri are nearly circular in basal section, 

 but gradually become slightly compressed laterally and are moderately compressed 

 in the distal portion; this lateral compression is very gradual, and is not accompanied 

 by an increase in the lateral diameter of the cirrus as in A. bifida. In a lateral view, 

 the dorsal profile of the segments is seen to be slightly more concave than the ventral, 

 especially distally, making the proximal and distal dorsal ends of the segments somewhat 

 prominent. 



The disk resembles that of A. mediterranea. It is usually naked, but sometimes has 

 more or fewer calcareous particles in the inner portion of the interambulacral areas. 

 Sacculi are abundant along the ambulacra, but small and irregularly arranged in one, 

 two or three rows, becoming more definitely arranged in a single row along the brachial 

 ambulacra. 



The radials in the median line are even with, or extending very slightly beyond, 

 the edge of the centrodorsal, rising in the interradial angles of the calyx into a low 

 triangle. 



The IB^ are oblong or slightly trapezoidal, two and a half to three tunes as 

 broad as long, the lateral edges slightly produced and swollen; a shallow groove usually 

 borders this swollen edge interiorly, which may be reduced to a small rounded pit just 

 proximal to the median horizontal diameter of the ossicle. The IBr 2 (axillary) is 

 roughly a right-angled triangle, the apex rather sharp; the lateral edges, which are 

 about half the length of those of the IBr,, are somewhat swollen and produced. 



The ten slender arms are up to 110 mm. long; the first brachial is wedge-shaped, 

 twice as long exteriorly as interior^, about half again as. broad as the exterior length, 

 interiorly just in contact basally; the exterior margin is swollen and slightly produced; 

 the second brachial is irregularly quadrate, larger than tho first, though of about the 

 same length exteriorly; synarthrial tubercles are sometimes slightly prominent, but 

 usually not marked; the third and fourth brachials (syzygial pair) are slightly longer 



