116 HAWAIIAN AND OTHER PACIFIC ECHINI. 



frequently so dark that their coloration is just like that of diadema. Doder- 

 lein (1902) has suggested that the two species may be distinguished by 

 the coloration of the primary spines of the ambulacra, which he says are dis- 

 tinctly banded in diadema and unicolor in calamaris. While this seems to be 

 true in most cases, we have found exceptions in both species, some specimens 

 of diadema having the annulations wanting (and they are often very faint), 

 while some specimens of calamaris have faint, but still distinct, indications of 

 the bands. As regards the tuberculation of the test, diadema rarely has more 

 than three primary tubercles on a coronal plate, while calamaris may have 

 five or even six ; but unfortunately most specimens of the latter have, like 

 diadema, only three, and occasional specimens of diadema have four. The 

 difference in the structure of the primary spines seems, however, to be re- 

 markably constant at all ages, and we therefore distinguish the two species 

 by that character. It seems to be true also that the tridentate pedicellarise 

 are constantly different and furnish an additional specific character. 



There are apparently only two species which can be constantly recognized 

 in the genus, both littoral and ranging throughout the Indo-Pacific region from 

 Zanzibar to the Society and Hawaiian Islands. The species Desorii Agasa. 

 seems to be undoubtedly a form of calamaris, probably the fully matured 

 adult; the essential structure of the spines and the pedicellariae are like 

 calamaris, and the differences in the test do not appear to be constant. We 

 distinguish calamaris and diadema as follows : 



Primary spines of interarabulacra rather solid, diameter of central cavity 

 much less than ^ diameter of spine; minute teeth covering spine, arranged 

 in crowded longitudinal series and not in distinct whorls ; blade of valves 

 of tridentate pedicellariae widest near middle diadema. 



Primary spines of interambulacra fragile, diameter of central cavity more 

 than \ diameter of spine ; minute teeth covering spine, arranged in dis- 

 tinctly separated whorls ; blade of valves of tridentate pedicellariae widest 

 at or near tip calamaris. 



Echinothrix diadema Lov^n. 



Echinus diadema Linnaeus, 1758. Sys. Nat., p. 664. 

 Echinothrix diadema Loven, 1887. Ech. desc. by Linn., p. 137. 



Tiiis species was taken by tlie '' Albatross" at the following stations: 



Puako Bay, Hawaii, Hawaiian Islands. 



Honolulu, Oahu, H. I. 



Papeete, Tahiti, Society Islands. Sept. 29 and Nov. 14, 1899. Reef. 

 Thirty-one specimens. 



