HOLOPXEUSTES PURPURESCENS. 485 



vertical rows. The tubercles of the interambulacral space form irregular 

 horizontal lines, with rather large miliaries and secondaries closely filling the 

 coronal plates, except a narrow, bare median band extending from the abac- 

 tinal pole half-way to the actinostome, where the band disappears. There 

 is one principal primary vertical row of large tubercles, between which and 

 the poriferous zone the secondaries and miliaries are very closely packed. 

 In the ambulacral space the tubercles are irregularly arranged, forming only 

 most indistinct vertical rows ; the tubercles are of more uniform size than 

 in the interambulacral space, and a comparatively greater number as large 

 as the primaries ; the tubercles do not increase in size towards the actino- 

 stome, as in Amblypneustes. The spines are shorter, rather stouter, than 

 those of Amblypneustes, and swelling at the extremity ; they are coarsely 

 striated longitudinally, the ridges forming small lamella? at the swollen ex- 

 tremity ; the shaft is very uniform in width, scarcely tapering towards the 

 extremity. Milled ring very prominent. Abactinal system with narrow 

 genital ring ; genital plates of uniform size ; large anal system ; genital pores 

 very large ; ocular plates prominent, excluded from the anal system. Anal 

 system and anal edge of the genital ring closely crowded by small tubercles, 

 carrying small spines similar to those of the test. Secondary tubercles 

 irregularly scattered over the whole poriferous zone. 



The ground-color of the test is greenish-blue, with violet median lines in 

 the ambulacral and interambulacral spaces ; the tubercles are of a lighter 

 color. The poriferous zone is light greenish with violet tinge. Spines 

 greenish at base, with reddish tinge towards the tip. 



Holopneustes purpurescens 



I Amblypneustes purpurescens Lutk., 1872, in A. Ac, Bull. M. C. Z., III. 

 ! Holopneustes purpurescens A. Ag., 1872, Bull. M. C. Z., III. 



PI. VI. f. 25-25*; PI V IIP. f. 5-6. 



Actinal and abactinal diameter equal, poriferous zone equal in width to 

 the corresponding tuberculiferous ambulacral space. In large specimens the 

 middle row of pores is very irregular, forming zigzag lines, while in younger 

 specimens the middle row is nearly as uniform as the inner and outer rows ; 



