ART. 5 ECHINODERMS FROM THE TONGA ARCHIPELAGO CLARK 5 



pletely with niathaei in each one of the characters, but are usually 

 easily distinguished by the combination of all five. They remarked 

 that such specimens occur only in material from the Hawaiian, 

 Society, and Philippine Islands. 



The si^ecimens from Niuafoou are very variable in every feature, 

 but those that are referable to ficta seem simply to represent the 

 younger or immature stages of the large ones, which are undoubtedly 

 referable to niathaei. 



In color the test is always dark, usually a more or less deep reddish 

 brown, though sometimes quite black. The spines may be light olive- 

 gray to deep olive, with long or short white or pinkish tips usually 

 preceded by a broad and indefinite very dark band; or fawn color, 

 uniform or with lighter or darker tips; or olive with fawn-colored 

 tips; or olive becoming gradually darker at the tips; or whitish 

 faintly tinged with olive or with fawn color. The milled ring is 

 almost always pure white, but is occasionally slightly tinged with 

 fawn color or pink. 



In some specimens, apparently from quiet water, the spines are 

 very slender and much elongated. 



ECHINOMETRA OBLONGA (de Blainville) 



Plate 5, Figtire 3 ; Plate 7, Figubb 3 



One hundred and seventy-eight specimens, most of which are young 

 of various sizes. 



Young individuals of this species (pi. 5, fig. 3; pi. 7, fig. 3) are 

 much flattened and broadened, the longer diameter being often but 

 slightly in excess of the shorter, and the spines are slender and rela- 

 tively long, and occasionally elongated. This gives them a consider- 

 able superficial resemblance to similarly small examples of Stomop- 

 neustes variolaris. 



The specimens are all very dark in color, purplish black or very 

 dark olive. The milled ring at the base of the primary spines is 

 usually pure white, sometimes white tinged with purplish, pinkish, 

 or olive. 



A specimen from Puako Bay, Hawaii, recorded by A. Agassiz and 

 H. L. Clark as Echinometra picta (U.S.N.M. No, 32813) seems to me 

 to be a young example of this species. 



ZENOCENTROTUS, new genus 



Diagnosis. — A genus of Echinometridae in which the longer axis, 

 which only slightly exceeds the shorter, passes through interambu- 

 lacrum 4a and ambulacrum Ila; the ambulacral plates consist of 

 9 to 11 elements ; the periproct is studded with numerous small plates ; 



