86 THE VOYAGE OF H.M.S. CHALLENGEK. 



of secondary and miliary tubercles, occupying the middle region of each plate, and 

 extending to the median line (PL XVIII. figs. 4, 5). On the ambulacral plates the 

 secondaries are distant and more irregularly arranged than on the interambulacral plates 

 (PL XVIII. fig. 1, 2, 4, 5). The coronal plates vary in colour from greenish to light 

 violet brown, the intervening bare spaces of the membrane of the test are of a milky 

 colour. 



The suckers of the tentacles are tipped with orange on the actinal side. The test of this 

 species is remarkably thin, even in the largest specimen (64 mm. in diameter), the cal- 

 careous plates do not give to the test any degree of solidity. In alcohol the general outHne 

 of the test is angular with rounded corners, and when seen in profile the edges of the test 

 are somewhat swollen, the test sinking below the level of the ambitus between it and the 

 actinostome, and also between the ambitus and the abactinal system. There are three 

 kinds of pedicellarise found upon the test resembling those of the test of Phormosoma. 

 The pointed suckers of the abactinal side are large, and commence close to the ambitus. 

 In Plate XVIII. fig. 6, the abactinal system has accidently been drawn out of line; the axis 

 passing through the madreporic body should be on the left to have it correspond with the 

 other figures of the abactinal system on the same plate. The larger primary spines, 

 especially those near the ambitus on the actinal surface, resemble somewhat the curved 

 trumpet-shaped hollow spines of Asthenosoma grubii; they are, however, longer, more 

 slender, and of a lighter colour and transversely l^anded with vermilion, the other 

 secondary and miliary spines of both areas are shorter, sharp pointed, and only a few of 

 the primary spines of the abactinal surface near the ambitus are trumpet-shaped ; the 

 otliers resemble the secondary spines, but are larger and comparatively stouter, and are 

 more or less irregularly banded with carmine. 



In young specimens (PL XVIII. figs. 1,2; PL XVIII." figs. 14, 15) the vertical row of 

 primary tubercles adjoining the poriferous zone is not as weU marked as in the older 

 specimens, nor are the horizontal rows of secondaries and miliaries well defined. In the 

 smallest specimens collected (PL XIX. fig. 1-3) the spines are transversely banded with 

 broad carmine rings. In young specimens the primary spines are proportionally longer, 

 but as in older specimens of this species they are cylindrical, scarcely tapering towards 

 the tip. The secondary and miliary spines are fine, sharp pointed and uniformly tapering. 

 The integument of the abactinal system nearly conceals the calcareous plates irregularly 

 arranged round the anal opening, and also encroaches considerably on the outer edges of 

 the plates of the genital ring. The ocular plates are pentagonal, horizontally elongate ; 

 the genital plates (PL XVIII. fig. 6) are pear-shaped, pointed towards the median inter- 

 ambulacral line. The genital and ocular plates carry two or three secondary tubercles 

 near the anal edge. 



In somewhat younger specimens the abactinal system is marked for the greater uni- 

 formity in the size of the genital and ocular plates (PL XVIII. fig. 3). 



