DIADEMA GLOBULOSUM. 115 



tures that it shares with Savignyi and combine to distinguish it from the 

 other members of the genus. 



This species was taken by the "Albatross" only at Easter Island. Dec. 

 21, 1904, littoral, one specimen. 



Diadema globulosum A. Ag, 



Diadema globulosum A. Agassiz, 1863. Bull. M. C. Z., I, p. 20. 



As pointed out by Mortensen, this species is very near Savignyi, and yet 

 the large tridentate pedicellariae, when fully developed, are so readily dis- 

 tinguished from those of that species that we are inclined to keep them sepa- 

 rate. The valves in globulosum are remarkably flat and very nearly straight, 

 with the blade broad but becoming distinctly narrower near the tip. The 

 example figured by Mortensen is not quite typical, as this narrowing is not 

 clearly shown. In some cases it is very marked, one might almost call it 

 abrupt ; but, unfortunately, it is not always so. Examination of the type- 

 specimen of D. nudum A. Ag. from Hong Kong shows that the pedicellariae 

 are like those of globulosum, and there seems to be no good reason why the 

 two should not be united under the latter name, which has four months' 

 priority. 



This species was taken by the "Albatross " only on the reef of Papeete, 

 Tahiti, Society Islands. " Albatross " collection. Sept. 29, 1899. One 

 specimen. 



ECHINOTHKIX. 



Peters, 1853. Monatsb. Berlin Akad., p. 484. 

 Type-species, Echinus calamaris Pallas, 1774. Spic. Zool., I, fasc. 10, p. 31. 



Typical examples of the two species belonging to this genus are so very 

 different from each other that their confusion seems impossible, but when a 

 large series of specimens of all ages and sizes is examined, the characters 

 which are supposed to separate them prove very inconstant, with the single 

 exception of the structure of the spines. Thus the color is ordinarily very 

 different, E. diadema being often uniform black, or with only faint indica- 

 tions of banding with light and dark shades on the spines, while E. calamaris 

 is often very light colored, with the interambulacral primaries beautifully 

 annulated and the ambulacral primaries a uniform pale yellowish-green ; 

 but young specimens of diadema are much lighter and have the spines as 

 distinctly annulated as calamaris, while large specimens of the latter are 



