116 HAWAIIAN AND OTHER PACIFIC ECHINI. 



while in the smaller specimen they are only 5, 9, and 7 mm. These figures 

 indicate- a wide degree of individual diversity in the species. The pores of 

 each pair are very near together while the successive pairs are rather far apart, 

 so that the distance between two pores vertically is distinctly greater than 

 that between two horizontally. As the pores are very small, the whole effect 

 is a very narrow poriferous area, not easily made out (PI. 153, fig. 5). 



The tuberculation of the test is rather scattered. Thus, there are only 

 about 25 primary tubercles in an area 5 mm. square on the abactinal surface 

 in an interradius while in E. depressa on a similar area there are about 50. More- 

 over in depressa the ridges between succeeding pore-pairs carry a single linear 

 series of 3-5 miliary tubercles, but in sternopetala these are quite wanting. 



The periproct (PI. 147, fig. 1) is obliquely placed at the posterior end of 

 the test (PL 153, figs. 6 and 7) but the degree of obliqueness shows great diver- 

 sity. In the holotype, the angle formed by the plane of the periproct and that 

 of the oral surface of the test is about 150° while in a second specimen it is only 

 about 130°. As usual in the genus, the periproct is covered by three large 

 plates, bearing both primary and miliary spines, and above these plates are a 

 considerable number of minute plates surrounding the anus itself. The peri- 

 stome is rounded-pentagonal, about 8 mm. wide by 5 mm. long; the most 

 marked angle is in ambulacrum III. The peristomal membrane seems to be 

 full of very minute calcareous plates, neither large enough nor sufficiently 

 crowded to form a pavement. 



The primary spines are smooth and terete, rather blunt, with about eight 

 longitudinal ridges; orally they are 2-4 mm. long but on the aboral surface, 

 they rarely exceed 1.5 mm. The miliary spines are about a millimeter long, 

 multiscalariform (with about 6 or 7 rods); the tips are slightly swollen or 

 expanded and the whole spine is more or less distinctly prickly, at least when 

 cleaned of its organic matter. 



Of pedicellariae, all three kinds occur but the triphyllous are few and hard 

 to find. The valves of the triphyllous (PL 144, fig. 20) are only .05 mm. long; 

 they are quite flat with serrate margins. The ophicephalous pedicellariae are 

 not rare; their valves (PL 144, fig. 21) are about .21 mm. long with the loop 

 .03-07 mm. more, and have a low, wide mouth which is quite distinctive. The 

 tridentate pedicellariae are very common and show great diversity in form of 

 valves and in size. The small ones are not peculiar, and their valves (PL 114. 

 fig. 24) are only .20-.25 mm. long. The largest, with valves (PL 144, fig. W) 

 over .60 mm., are very characteristic; the margins of the valves are coarsely 



