ART. 6 ECHINODEBMS FROM THE TONGA ARCHIPELAGO CLARK 1 1 



In the smallest the longer diameter of the test is 25 mm., and the 

 longest spines are 20 mm. long. 



These specimens, most of which are small, show very great diver- 

 sity. In the largest (pi. 8, fig. 1) the primary spines near the center 

 of the apical surface are very stout at the base, regularly tapering 

 and conical, and up to 57 mm. long. Toward the ambitus the pri- 

 mary spines gradually increase in length, reaching a maximum of 75 

 mm., and at the same time gradually become rounded trigonal with 

 somewhat blunted tips. The secondary spines for the most part are 

 stout and sharp pointed, but those on the apical disk are very short 

 and abruptly truncated. 



In three other specimens the primary spines are rather slender, 

 tapering, and trigonal. In one there are a few short and abruptly 

 truncated spines on and about the periproct and in the upper por- 

 tions of the ambulacral areas ; in another short and irregularly trun- 

 cated spines are rather numerous on and about the apical system; 

 while in the third such spines are very numerous. 



In all the other specimens {cf. pi. 4, fig. 2 ; pi. 8, fig. 2) the primary 

 spines are thickened, more or less club shaped, with abruptly rounded 

 tips. In some the large primaries of the ambulacral areas run up 

 almost to the oculars, while in others a large portion of the ambulacral 

 areas on the apical surface is covered simply with short abruptly 

 truncated spines, which in extreme cases may extend nearly to the 

 ambitus as in H. mamtiiillatus. 



Class ASTEROIDEA 

 Family ARCHASTERIDAE 



ARCHASTER TYPICUS MiiUer and Troschel 



Nukualofa Island. One specimen. 



LINCKIA LAEVIGATA (Linnaeus) 



Seventeen large specimens. 



LINCKLA. MULTIFORA (Lamarck) 



Nukualofa Island. Two small specimens. 



EXPLANATION OF PLATES 



Plate 1 



Zenoeentrotus kellersi, the type specimen, Niuafoou, October 6, 1930 (U.S.N.M. 

 No. E. 2810), apical view, X2. Oral view of the same specimen shown ia 

 Plate 2. 



Plate 2 



Zenoeentrotus kellersi, the type specimen, Niuafoou, October 6, 1930 (U.S.N.M. 

 No. E. 2810), oral view, X2. Apical view of the same specimen shown in 

 Plate 1. 



