A MONOGRAPH OF THE EXISTING CRINOIDS 235 



distal ends, as do the segments of all the pinnules except in the distal portion of the 

 first 1 or 2. 



The color in alcohol is white, yellowish white, or violet, the cirri and pinnules 

 dark purple with the ends of the segments white, in sharp contrast. 



Notes. The specimen from Antigua has 19 arms. 



Hartlaub described this species, under the name of Actinometra echinoptera var. 

 discoidea, on the basis of 5 specimens which he found in a single jar labeled in Car- 

 penter's hand "Actinometra discoidea." There were 3 locality labels in the jar, 

 Montserrat, 88 fathoms [Blake station 155], Martinique, 96 fathoms [Blake station 

 203], and Dominica, 118 fathoms [Blake station 177]. In addition to these he had 

 2 very young specimens, one from St. Vincent [Blake station 231] and the other from 

 Montserrat, 88 fathoms [Blake station 155]. 



His largest specimen, which he described in very considerable detail, represents 

 not this species but N. iowensis. 



Hartlaub says that the most striking features of discoidea are a plating of the 

 dorsal interradial perisome and a dark brown spotting of the pinnule segments, the 

 distal ends of which are everted and finely spinous. 



Four of the specimens studied by him lacked the interradial plating of the disk 

 and possessed strong carinate processes on the basal segments of the proximal pinnules 

 resembling those seen in Leptonemaster venustus. He noted that the interradial plat- 

 ing is also found in rubiginosa ("lineata"), though not constantly, and in this species 

 also the basal segments of the lower pinnules are sometimes slightly carinate. 



The centrodorsal is medium sized, always flat, discoidal, sometimes bluntly 

 pentagonal, always with the cirrus sockets in a single marginal row. 



The segments in a well-developed cirrus from a small specimen from Blake 

 station 155 number 19. In general the cirri resemble those of Leptonemaster venustus 

 except for the somewhat elongate 2 basal segments. 



The radials are visible. The IBri and IBr 2 are somewhat longer than in N. iowen- 

 sis. The IBr series are not in lateral contact, but the perisome between them is plated. 

 The IIBr series are 4 (3+4). All the division series have the dorsal surface smooth 

 and strongly rounded. The component segments have only very slightly produced 

 ends. Synarthrial tubercles are sometimes feebly developed. There are no IIIBr 

 series. 



Hartlaub figured a very young specimen with 1 1 arms from Blake station 23 1 in 

 which the interradial perisomic plating is very well developed. 



The largest specimen examined by Hartlaub had 14 arms, four of the postradial 

 series having 3 arms each and the fifth 2. 



The next smaller, which had at least 17 arms, had 3 postradial series with 4 arms 

 each. 



A younger example had 2 postradial series with 4 arms, two with 3 arms, and one 

 with only 2 arms, making 16 arms in all. 



A still younger specimen had all of the postradial series with 2 arms. 



The arms are rather slender at the base, and taper sometimes rather rapidly 

 and sometimes very gradually. 



The brachials up to the sixth are quadrangular, those following becoming rather 

 markedly wedge-shaped, although not triangular. After the tenth the brachials 



