276 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



fAntedon laevissima Brit. Mus., MS. A. H. CLARK, Smithsonian Misc. Coll., vol. 61, No. 15, 1913, 



p. 23 (Fadiffolu, Maldives) . 

 Heterometra producta A. H. CLARK, Unstalked crinoids of the Siboga-Exped., 1918, p. 76 (in key; 



range). GISLN, Kungl. Fysiogr. Sallsk. Handl., new ser., vol. 45, No. 11, 1934, p. 22. A. H. 



CLARK, John Murray Exped. 1933-34, Sci. Reports, vol. 4, No. 4, 1936, p. 99 (range), p. 103. 



Diagnostic features. -The enlarged proximal pinnules are rather slender and 

 become flagellate distally; their basal segments are sharply carinate, and the seg- 

 ments from the third onward have the entire distal end somewhat produced and over- 

 lapping, the outer portion of the prismatic ridges being produced into a blunt spine 

 which is directed obliquely forward. The cirri have 23-26 segments of which the 

 longest are half again as long as broad, and the outer are about as long as broad. 

 The 10-13 arms are 50 mm. long. 



Description. The centrodorsal is low hemispherical, almost discoidal; the polar 

 area is moderate in size with a raised and rotighened center. The cirrus sockets are 

 arranged in two crowded alternating rows, beyond which are one or two rows of more 

 or less obliterated sockets. 



The cirri are XVI, 24-26, slender, 15 mm. long. The first three segments are 

 very short, the fourth is not quite twice as broad as long, the fifth-eighth are half 

 again as long as broad, and those following gradually decrease in length, after the 

 tenth or eleventh being about as long as broad. The ninth and following segments 

 are sharply carinate dorsally, and on some of the cirri bear small subterminal dorsal 

 spines. The opposing spine is terminal, rather large, and arises from the whole dorsal 

 surface of the penultimate segment, its distal edge being a continuation in a straight 

 line of the distal edge of that segment. The terminal claw is somewhat longer than 

 the penultimate segment, rather slender and moderately curved. 



The radials are short, with the middorsal line parallel to the dorsoventral axis of 

 the animal. The IBr t are very short, four or five tunes as broad as long. The IBr 2 

 (axillaries) are broadly pentagonal, rather over twice as broad as long, rising to a slight 

 smooth rounded tubercle with the IBr^ Three IIBr series are present in the type 

 specimen, all 4(3+4). 



The 13 arms in the type specimen are 50 mm. long. The first two brachials are 

 wedge-shaped, the next six are oblong, three or four times as broad as long, and those 

 following are short wedge-shaped, after about the middle of the arm becoming oblong 

 again and very short. 



PI is slender, becoming flagellate distally, 5 mm. long with 17-20 segments of which 

 the first is not so long as broad, the second-fifth are about as long as broad, and those 

 following become elongated and about twice as long as broad distally; the first seven 

 or eight segments are somewhat carinate. P 2 is similar to PI, 7 mm. long, with the 

 distal segments somewhat longer and the carination of the basal segments more 

 marked. In addition to the dorsal carination there is a lateral carination, which is 

 only slightly marked on PI, especially evident toward the end of each segment. P 3 is 

 comparatively stout and stiff, 8 mm. long with 12 segments of which the first is not 

 quite so long as broad, the second is about as long as broad, and those following become 

 elongated, being about three tunes as long as broad distally. The second-fifth seg- 

 ments have a sharp dorsal keel, and from the third onward the median portion of the 

 outer surface of the distal ends of the segments is produced, forming a moderate lateral 



