AET. 5 ECHINODERMS JTEOM THE TONGA ARCHIPELAGO CLARK 9 



upper side is less evenly rounded, being highest in the center, the 

 cross section being a more or less low triangle with broadly rounded 

 angles, the upper obtuse angle becoming less and less marked dis- 

 tally. The spines are about 2.5 mm. broad with parallel sides and 

 an abruptly truncated tip. Just below the ambitus the spines are 

 somewhat shorter and more flattened, and broaden slowly from the 

 base to the distal half or two-thirds. On the oral surface they 

 are abruptly shorter, and they rapidly decrease in size adorally, 

 becoming at the same time much more slender. 



Above the ambitus the primary spines decrease in length and 

 become less flattened and more pointed, tapering evenly from the 

 base to the somewhat blunted tip and being more or less regularly 

 rounded in cross section. The spines on the third interambulacral 

 plates below the apical disk are 13 to 15 mm. long. 



Interspersed with these large spines are great numbers of much 

 smaller spines from 3 to 5 mm. in length. These are mostly, 

 especially along the poriferous zones, club shaped, slowly increasing 

 in diameter to an abruptly truncated tip. A few of the larger ones 

 have parallel sides, and some taper to a blunt tip. 



The primordial ambulacral plates are rounded wedge shaped, the 

 two of each pair with their larger ends together, forming a closed 

 ring about the mouth. They are studded with tubercles and bear 

 small blunt spines and numerous pedicellariae. Frequently very 

 small nonambulacral plates are intercalated between these pairs of 

 ambulacrals. 



The peristomal membrane is thickly set with very numerous very 

 small and greatly elongated plates arranged concentrically, and it 

 also bears a few widely scattered small rounded plates each with 

 a median tubercle and spine and a thickened rim. 



The teeth are much flattened and very thin, as in Podophora^ with 

 a narrow elevated rim bordering the flat upper surface on each side. 

 In section the teeth are flattened trapezoidal. 



The color is dull olive-brown with a tinge of purplish, the long 

 spines at the ambitus lighter below and outwardly more or less 

 strongly tinged with violet. 



ry/)e.— U.S.N.M. No. E. 2810, collected at Niuafoou by Lieut. 

 H. C. Kellers on October 6, 1930. 



Six additional specimens were collected on October 5 and 6, 1930. 



Notes. — In the largest specimen (pi. 4, fig. 1; pi. 5, fig. 1) the 

 longer diameter of the test is 60 mm., and the shorter diameter is 

 55 mm. ; the height of the test is 25 mm. The longest spines at the 

 ambitus are 30 mm. and the spines near the apical disk are 15 mm. 

 long. The color is dull olive, the longest spines tinged with violet 

 toward the tip; the spines at and below the ambitus have violet 

 tips beneath. 



