Boone, Echinodermata, Cruises of "Ara" and "Alva" 171 



Pacific to the Fiji, Marshall, Gilbert and Hawaiian Islands, Guam, 

 Laysan and Palmyra Islands, and also throughout the northern 

 coast of Australia, the Malay Archipelago, Macclesfield Bank, the 

 Bonin Islands and Japan . Although it is principally a dweller in 

 the littoral zone, being found abundantly on the reefs, tidepools 

 and among the coral heads, it is also found in deep water down to 

 about 300 fathoms. Messrs. Agassiz and Clark had a series of 

 296 specimens taken by the "Albatross" dredgings of 1902 in 

 Hawaiian waters, the vicinity of Laysan and off French Frigate 

 Shoal in bathymetric range of 13 to 319 fathoms, and temperature 

 extremes of 78.9 to 67 degrees. 



Material examined: Four specimens taken in Pearl Harbor, 

 Oahu, Hawaiian Islands, in two fathoms, December 14, 1928. 



Colour: Deep-water specimens reddish to purplish brown; 

 young, brighter than older forms ; The primaries are purplish 

 brown with three or four white rings. The median interambu- 

 lacral space and some of the scrobicular spines are pearly white, 

 contrasting sharply with the dark background. The apical sys- 

 tem is light, or white, or entirely dark, or sometimes with the dark 

 plates strikingly margined with white lines between them. 



Technical description : This species has been exhaustively 

 analyzed with exquisite illustrations of both larval and adult 

 forms by Dr. Theodore Mortensen (1921 and 1928) . 



Metidaria is the only one of the five members of the genus 

 Eucidaris Pomel known from the great area of the Indo-Pacific 

 region. This species is quite small in comparison with the com- 

 mon species of the tropical and subtropical west coasts of the 

 Americas, or the better known E. tribuoides of tropical and sub- 

 tropical east American waters. Eucidaris metvlaria is readily 

 recognized by the distinctive primary spines, which are clavate, 

 of moderate diameter for this genus, their length usually being 

 less than the horizontal diameter of the test, thickened proximally 

 and attaining the greatest width about one-third of the length from 

 the proximal end, gently tapered, the shaft bearing low spinules 

 arranged in 12 to 18 longitudinal series, these converging on the 

 apex to outline a crown, the center of this apex being a distinct 

 rounded knob. In the eroded apices of the primaries, especially 

 of littoral specimens, this knob and related coronal pattern are 

 frequently lost, the eroded apex being rounded or even subtrun- 

 cate, smooth. 



