A MONOGRAPH OF THE EXISTING CRENOIDS 131 



segment beyond the transition segment prominent median terminal spines begin to 

 appear; these gradually come to involve more and more of the dorsal surface of the 

 segments, which becomes carinate, so that after the twenty-third the dorsal profile is 

 straight and parallel to the longitudinal axis of the cirrus as a whole. In the next 

 four to seven segments a shallow rounded notch is developed in this straight dorsal 

 profile so that the segments appear to have both a proximal and a distal spine. Be- 

 yond this point the dorsal processes are of the high strongly carinate type common to 

 the other species of the genus. 



The ends of the basal rays are visible in the interradial angles of the calyx just 

 over the ends of the ridges separating the individual columns of cirrus sockets in the 

 interradial pairs; they appear as small dorsoventrally elongated tubercles. 



The radials are almost entirely concealed. They bear on their apposed edges, 

 just over the ends of the basal rays, two tubercles or blunt spines, one on each radial. 

 Owing to the depth of the midradial furrows on the centrodorsal the subradial clefts 

 are practically obsolete, only their inner ends being visible as very narrow and very 

 shallow grooves. The IBri are extremely short, six or more times as broad as long, 

 chevron-shaped, with both the anterior and posterior edges prominently everted and 

 smooth, somewhat wavy, or coarsely tubercular; in the middorsal line there is a 

 prominent median rounded carination. 



The IBr 2 (axillaries) and arms are lacking. 



Notes. A smaller specimen found with the type appears to represent a younger 

 stage of the same species. The centrodorsal is truncated conical, 3.5 mm. in diame- 

 ter at the base and 1.5 mm. broad at the dorsal pole; the height is 3 mm. measured 

 along the inclination of the sides. The dorsal pole is covered with short spines. In 

 general the centrodorsal resembles that of the other specimen, but owing to its conical 

 shape the midradial furrows converge distally. 



The cirri are about 40 mm. long and are composed of 54-58 segments of which the 

 sixth is a transition segment. 



The ends of the basal rays are rather more prominent than they are in the other 

 specimen. 



The radials are smooth, without lateral spines. The IBr! have scarcely a trace 

 of the eversion of then- edges, but possess a higher and sharper median keel, and usually 

 also a sharp tubercle on the distal border about one-third the distance between the 

 distal lateral angle and the median line. The IBr 2 (axillaries), which are missing in 

 the other specimen, are approximately triangular (though probably shield-shaped as in 

 other species of the genus when fully grown), twice as broad as long, with a high and 

 sharp carination in the proximal two-thirds of the median line and with everted and 

 spinous distal edges. 



On one of the postradial series the IBr 2 is not axillary as usual but bears a pinnule 

 which is essentially similar to P : in related species; the second segment beyond this is 

 axillary; there is no carination beyond the first pinnule. Only two axillaries are pre- 

 served, both detached. One has lost both derivatives at the first postaxillary articu- 

 lation; the other bears on one side one and on the other side three brachials. 



Locality. Investigator station 232; Laccadive Sea (kt. 717'30" N., long. 7654'30" 

 E.); 786 meters; (A. H. Clark, 1912, 1918] (2, U.S.N.M., 35593; I. M.). 



