A MONOGRAPH OF THE EXISTING CKINOIDS 247 



Diagnosis. A genus of Colobometridae including small and delicate species with 

 10 arms 12-35 mm. long; P! and P a are absent; and the cirri are composed of 12-19 

 segments which bear dorsally a curved transverse ridge, becoming outwardly a single 

 median tubercle. 



Geographical range. From southwestern Mindanao to the Bonin Islands. 



Batkymetrical range. From 72 to 80 meters. 



Remarks. Dr. Gisl6n placed this genus in the subfamily Perometrinae of the 

 family Autedonidae. But the transverse ridge on the cirrus segments, the stout 

 cirri composed of segments most of which are about as long as broad, and the general 

 structure seem to me to place it in the family Colobometridae. The features resem- 

 bling more or less closely those characteristic of the Perometrinae are in my opinion 

 due simply to the small size. Clarkomctra elegans resembles the small species of the 

 genera Decametra and Prometra much more closely than it does any of the species 

 included in the subfamily Perometrinae. 



Gislen said that in all morphological characteristics Clarkometra proves to be a 

 macrophreate type and is to be included in the subfamily Perometrinae. But he 

 noted the fact that the dorsal prominence on the fifth-eighth cirrus segments is a 

 transversely curved even crest and remarked that this reminds one of the condition 

 in the family Colobometridae where, however, the crest is always forked or serrate. 

 He wrote that Clarkometra agrees with the genus Hypalomelra in the absence of P! 

 and P a , but differs from it in the low flattened centrodorsal, the short cirri which are 

 composed of a rather small number of approximately squarish segments, and in the 

 occurrence of two pairs of oral pinnules. Of the other distinguishing marks he said 

 he ought, perhaps, to mention the appearance of the cirrus sockets on the centrodorsal. 

 The perforation for the central canal is situated in the middle of a relatively large 

 calcareous wart located in the central part of the cavity in which the cirrus is fixed. 



CLAREOMETRA ELEGANS Glsln 



PLATE 26, FIGURES 137, 138 



Clarkometra elegans GISLN, Nova Acta Reg. Soc. Sci. Upsaliensis, ser. 4, vol. 5, No. 6, 1922, p. 5 

 (127-163 m.), p. 6 (Bonin Islands), p. 143 (descriptions of 17 specimens; Bock's stations 43, 53), 

 pp. 182, 183 (listed), figs. 141-149, p. 146, pi. 1, fig. 8; Zool. Bidrag Uppsala, vol. 9, 1924, p. 39, 

 footnote (disk reaches to brachials 3 + 4), p. 42 (brachial angles), p. 44 (reversion), pp. 46, 47, 

 51 (obliquity of joint faces), p. 53 (axillary angle), p. 82 (syzygies), fig. 10, p. 45 (arm base), figs. 

 30-32, p. 52, fig. 84, p. 81. A. H. CLARK, Temminckia, vol. 1, 1936, p. 295 (listed), p. 310 

 (Willebrord Snellius station 60*; notes). 



Description. The centrodorsal is low and convex, 1.8 mm. broad and 1 mm. high 

 from the radials to the dorsal pole, with the bare dorsal surface 1 mm. in diameter and 

 somewhat granulated. The cirri are arranged in two crowded alternating rows. 



The cirri are XXX, 15-18, from 3.5 to 5 mm. long. The first segment is broader 

 than long, the second and third are about as long as broad, and the fourth is one- 

 quarter again as long as broad. The segments succeeding decrease in length. The 

 fifth-seventh or eighth segments have a low curved transverse ridge which beyond the 

 eighth contracts to a small simple dorsal tubercle. The opposing spine is sharp and 

 rather large, reaching a height equal to half the width of the penultimate segment. 

 The terminal claw is about as long as the penultimate segment and is curved and rather 

 stout. The cirri as a whole are rather stout. 



