STRONGYLOCENTROTUS NUDUS. 363 



The test is 73 mm. in diameter and 40 mm. high. When compared with a 

 specimen of drobachiensis of the same size, the only noticeable difference, aside 

 from the characteristic coloration, is the smaller size and larger number of the 

 primary tubercles, and spines. There are 25 or 26 interambulacral plates, and 

 39 or 40 ambulacral, in each column, while in a drobachiensis, 75 mm. h. d. and 

 42 mm. high, the numbers are 22 and 38 respectively. The primary spines of 

 the latter specimen are 11 or 12 mm. long, while those of polyacanthus are only 

 6-8 mm. The arc of pore-pairs are essentially as in drobachiensis, oblique 

 approaching the horizontal, and with only six pairs in each arc. The test and 

 spines are uniformly dull rose-purple, without a trace of green. 



The pedicellarise show some characters which may prove to be of importance. 

 The globiferous are all small and the valves (PI. 94, figs. 31, 32) have a short 

 terminal tooth; they are about .50 mm. long with the terminal tooth scarcely 

 one fourth as much. The ophicephalous are peculiar in that the valves (PI. 94, 

 fig. 33) which measure .40-.60 mm. in length, are not at all constricted but are 

 bluntly triangular in form; the articular loops are also noticeably low and 

 flattened. The tridentate pedicellarise (PI. 94, fig. 30) are all rather long and 

 narrow; none of those, so common in drobachiensis, with broad curved blades, 

 were found; the valves are .40-1.60 mm. in length and are more or less fully 

 in contact throughout. The triphyllous are very common and show some 

 diversity in the relative width of the blade; the valves are about .15 mm. long. 

 The calcareous spicules are either bihamate or curved rods with branched ends. 



The single specimen of this species was taken by the collectors of the " Alba- 

 tross" on the shores of Milne Bay, Simushir Island, Kuril Group, Northern 

 Japan, June 23, 1906. 



Strongylocentrotus nudus A. Ag. 



Toxocidaris nuda A. Agassiz, 1863. Proc. Acad. Nat. Sci. Philadelphia, p. 356. 

 Strongylocentrotus nudus A. Agassiz, 1872. Rev. Ech., pt. 1, p. 165. 

 Strongylocentrotus hokkaidensis Doderlein, 1906. Zool. Anz., XXX, p. 518. 

 Strongylocentrotus tuberculatus A. Agassiz and Clark, 1907. Bull. M. C. Z., LI, p. 122. NON 

 Echinus tuberculatus Lam'k. 



Plate 94, figs. 17-23. 



In view of the fact that this species is now known to be one of the common 

 sea-urchins of northern Japan but does not appear to occur in the warmer south- 

 ern seas of that country, it seems very probable that the original specimens, 

 brought home by the United States Exploring Expedition and described in 

 1863, were all from Hakodate and not in part from Hilo, Hawaii, as they were 



