A MONOGRAPH OF THE EXISTING CRINOIDS 139 



OCEANOMETRA GIGANTEA (A. H. Clark) 



PLATE 14, FIGURE 41 



[See also vol. 1, pt. 1, figs. 203, p. 239, 364, p. 297; pt. 2, figs. 145, 146, p. 83, 220, p. 168, 284, p. 255, 

 322, 332, p. 227, 344, p. 229, 859-866, p. 419.] 



Thalassometra gigantea A. H. CLARK, Proc. U. S. Nat. Mus., vol. 34, 1908, p. 214 (in key), p. 222 

 (description; Albatross station 3985); vol. 35, 1908, p. 121 (proximal ornamentation; arm struc- 

 ture); Araer. Nat., vol. 42, No. 500, 1908, p. 542 (belongs to a group characteristic of the oceanic 

 area); Geogr. Journ., vol. 32, No. 6, 1908, p. 603 (same); Proc. Biol. Soc. Washington, vol. 22, 

 1909, p. 14 (listed); Proc. U. S. Nat. Mus., vol. 39, 1911, p. 551 (nearest to Th. [Oceanomelra] 

 annandalef) ; Zool. Anz., vol. 39, No. 11/12, 1912, pp. 425, 426 (compared with Th. [Oceanomelra 

 magna); Crinoids of the Indian Ocean, 1912, p. 203 (synonymy; locality); Die Crinolden der 

 Antarktia, 1915, p. 124 (shows the characteristic features of Anthometra adriani). 



Oceanometra gigantea A. H. CLARK, Journ. Washington Acad. Sci., vol. 6, No. 17, 1916, p. 606 (listed); 

 Unstalked crinoids of the Siboga-Exped., 1918, p. ix (relationship with 0. magna), p. 150 (in 

 key; range), p. 151 (references). GISLEN, Kungl. Fysiogr. Sallsk. Handl., new ser, vol. 45, No. 

 11, 1934, p. 27. A. H. CLARK, Bernice P. Bishop Mus. Bull. 195, 1949, p. 74 (Albatross station 

 3985), p. 99 (station data). 



Diagnostic features . The second, but not the first, clement in the pairs of ossicles 

 in the division series, and the second, but not the first, brachials bear a high sharp 

 median keel. This is a large and stout species with 17 arms 180 mm. long, and the 

 stout cirri 75 mm. long with 48-62 (usually 55-60) segments. 



Description. The centrodorsal is a truncated cone 10 mm. broad at the base, 10 

 mm. high, and 3 mm. across the broad and flat dorsal pole. Its surface is divided into 

 5 radial areas by 5 narrow, but high, interradial ridges. The cirrus sockets are ar- 

 ranged in 2 columns of about 4 each in each radial area, the 2 columns in each radial 

 area being separated by a bare area which in width is equal to about three-quarters 

 the transverse diameter of the sockets, or twice the width of the interradial ridges. 

 The bare areas in the midradial line between the columns of cirrus sockets, the inter- 

 radial areas, and the distal half of the centrodorsal, which bears no cirri, have a rough 

 and uneven surface and are thickly covered with small spines. 



The cirri are XL, 48-62 (most commonly 55-60), 75 mm. in length. The first 

 segment is very short and those following gradually increase in length so that the fifth 

 is about as long as broad and the ninth is about twice as long as its proximal width. 

 The tenth segment is about half again as long as broad and those succeeding slowly 

 decrease in length, the sixteenth and seventeenth being about as long as broad, the 

 distal broader than long, and the terminal about twice as broad as long. The basal 

 segments are broad in lateral view, but after the sixth they decrease rather rapidly in 

 width. The ninth segment is broader proximally than distally; its distal end is en- 

 circled by a narrow band with a polished surface resembling that of the succeeding 

 segments, the remainder of the surface being dull like that of the segments preceding. 

 The tenth and following segments are laterally- compressed. After the eleventh or 

 twelfth a dorsal keel begins to develop which soon becomes high and gradually takes 

 the form of carinate dorsal spines with a long dorsal crest which is parallel to the axis 

 of the segments, the dorsal crest becoming shorter and the processes more spinelike 

 as the segments decrease in length. The opposing spine is triangular, arising from 

 nearly the whole of the dorsal surface of the penultimate segment, and short, not 

 reaching half the width of the penultimate segment in height. The terminal claw is 



