822 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Description of the type specimen of Atelecrinus sulcatus. The centrodorsal is 

 sharply conical, 3 mm. broad at the base and 4 mm. high. The cirrus sockets are 

 arranged in 10 columns of 4, more rarely 5, each, the 2 columns of each radial area 

 close together, the pairs of columns in each radial area separated from those in the 

 adjacent radial areas by shallow furrows which proximally are in width nearly equal 

 to the width of the neighboring cirrus sockets, but become gradually narrower distally. 

 The interradial separation of the columns of cirrus sockets is always somewhat greater 

 than the midradial separation. Each cirrus socket is bordered proximally and laterally 

 by a horseshoe-shaped rim which proximally scarcely rises above the general surface 

 of the centrodorsal, but on either side stands out as a high ridge so that in lateral view 

 the profile of the centrodorsal appears strongly serrate, the longer side of the teeth 

 being gently convex and roughly parallel with the dorsoventral axis, the shorter slightly 

 concave and at right angles to this axis. The ridges on either side of the cirrus sockets 

 gradually increase in thickness distally, but terminate rather abruptly just after attain- 

 ing their maximum height and thickness so that the border of the cirrus sockets distal 

 to them is not raised above the general surface of the centrodorsal. The basal outline 

 of the centrodorsal as viewed dorsally is pentagonal, each side of the pentagon being 

 slightly and evenly concave. Five well-marked rounded interradial ridges are present 

 which slowly decrease in height and disappear at about the distal border of the first 

 cirrus sockets. These ridges mark the angles of the pentagon when the centrodorsal 

 is viewed dorsally. Their height is scarcely more than sufficient to modify the nor- 

 mally circular base of the centrodorsal to a pentagon. 



The basals form a very narrow band of almost uniform height between the radials 

 and the centrodorsal, though they are slightly higher in the angles of the calyx where 

 their exterior surface is raised to form a proximal continuation of the interradial ridges 

 on the centrodorsal. 



The radials are relatively long, distally not quite twice as broad as the median 

 length. The profile of the dorsal surface is straight. The proximal edge is somewhat 

 shorter than the distal. 



The IBr] are regularly oblong, about a third again as broad as long, entirely free 

 basally. There is almost no incision of the distal border but the distal lateral angles 

 are slightly cut away. The IBr 2 (axillaries) are broadly pentagonal, slightly broader 

 than long. Their lateral edges slope slightly inward and downward so as to form, 

 with the truncated distal corners of the IBi^, prominent water pores. Similar water 

 pores occur between the first and second brachials above the distal angles of the 

 axillaries. 



The 10 smooth, straight-sided arms resemble those of the type of wyvilli itself. 



Syzygies usually occur between brachials 3+4, 6 + 7, and 10 + 11 (or 9 + 10 on 

 two arms), and distally at intervals of 3 or 4 muscular articulations. The width at 

 3+4 is 1.9 mm., the length from IBr, to 6 + 7 is 9.5 mm. and to 10 + 11 is 13.5 mm. 



The lowest pinnule, on two arms, is on the sixteenth brachial. The pinnules 

 are small and weak, long jointed and strongly flattened. 



The visceral mass is high and narrow, and the ambulacral grooves reach the arms 

 along the summits of perisomic bridges as in Gephyrocrinus and in Thalassocrinus. 

 The mouth is central. The disk is unplated. 



Notes. A specimen dredged by the Albatross at station 5619, near the locality 

 (station 85) where the type of A. sulcatus was taken by the Siboga, appears to belong 



