STEREOCIDARIS LEUCACANTHA. 23 



Station 3919. Off Diamond Head, Oaliu. Bott. temp. 45.6'. 220-207 

 fathoms. Gy. s. 



Station 4044. Off Kavvaihae Light, "W". coast of Hawaii. Bott. temp. 

 47'. 198-233 fathoms. Fne. gy. s. 



Station 4096. Off Mokuhooniki Islet, approach to Pailolo Channel. Bott. 

 temp. 45.3°. 272-286 fathoms. Fne. gy. s. 



Bathymetrical range, 83-286 fathoms. Extremes of temperature, 

 47°-45.1°. Fifteen specimens. 



Stereocidaris leucacantha A. Ag. and Clark. 

 Plates 6 ; 15 ; 32. 



The specimens collected vary in diameter from 52 mm. (PI. 32, figs. 

 1-li) to 26 mm. They are notable for their long, slender primary radioles. 

 In a specimen measuring 28 mm. in diameter, the longest radioles are 

 67 mm. In a larger specimen, 37 mm. in diameter, the longest radioles 

 measure 87 mm.; they vary in color from light violet-gray to white, 

 with the band above the milled ring more or less distinctly purple. This 

 species is closely allied to 8. grandis, but the radioles (PL 6, fig. 8) differ 

 from those of that species in being more slender and more cylindrical 

 (Pis. 15, figs. 1, 2 ; 32, figs. 5, 6). The fluted extremity often expands 

 somewhat. 



The serrations of the radioles of leucacantha are smaller and less distinct 

 than those of grandis. The secondary spines both in the ambulacral and 

 interambulacral areas are shorter and smaller than those of grandis. The 

 granulation of the abactinal system and of the test is much closer and 

 smaller in this species than in grandis. (Compare Pis. 15 and 32 with 

 Pis. 33 and 36). The plates on the angles of the anal pentagon are much 

 larger than the corresponding plates of grandis. With increasing size the 

 ocular plates become more elongate (compare fig. 5, PI. 32, with fig. 1, PI. 32). 

 The large specimen figured on PI. 32, figs. 1-J^ shows an extraordinary 

 splitting of the upper interambulacral plate (PL 32, fig. 1) so that the 

 abactinal circle of interambulacral plates consists of fifteen plates instead 

 of ten, a structure we have not noticed in any other Cidarid. In another 

 specimen, from Station 3992, the abactinal edges of the plates which are split 

 have been pushed out by the genital and ocular plates, forming a steep wall 

 round the abactinal system, which thus bulges as much as 10 mm. well up 



