280 THE VOYAGE OF H.M.S. CHALLENGER. 



1. Calliaster baccatus, n. sp. (PI. LVI. figs. 1-4). 



Rays five. R= 44 mm. ; r = 18 mm. Breadth of a ray at the fourth marginal plate, 

 10 '5 mm. 



Rays short and of almost uniform breadth throughout after the basal expansion is 

 passed ; extremities obtuse. Interbrachial arcs widely rounded. Lateral walls rather 

 thick and vertical. Abactinal area more or less inflated. 



The abactinal area is covered with rather large, irregularly circular tabula, the medio- 

 radial series and the primary apical plates being the largest, and all diminishing in size as 

 they recede from the centre. Each plate bears on its tabulum a large robust, thimble-shaped 

 granule or stumpy spinelet, or, very rarely, two smaller ones may be present. The margin 

 of the tabulum is surrounded by a ring of comparatively large and somewhat irregular 

 bead-like granules of low elevation, somewhat flattened from the outside, having the 

 appearance of being skin-covered, and consequently rather badly defined. They suggest 

 in a certain degree the granules which bound the scrobicular ring around the primary 

 tubercles of most of the Cidaridse. In the interspaces between the plates small papulae 

 may be seen. 



The marginal plates are massive, and each is distinctly tumid, especially in the supero- 

 marginal series. The supero-marginal plates are nine in number, counting from the 

 median interradial line to the extremity, and exclusive of the odd terminal plate. They 

 form a broad conspicuous border to the disk and rays, the breadth of which increases 

 slightly as it approaches the extremity. The plates adjacent to the median interradial 

 line have the length subequal to, or slightly greater than, the breadth as seen from above, 

 but at the extremity of the ray these proportions are reversed, and the breadth is distinctly 

 in excess of the length. The penultimate plate is the largest of the series, and touches the 

 corresponding plate of the other side of the ray in the median line. The last paired plate is 

 small and wedge-shaped, and the odd terminal plate is small and more or less tubercle-like. 

 The surface of the plates is perfectly smooth, and their margin is surrounded by a single 

 series of rather large, flattened, bead-like granules. Each plate, excepting the innermost, 

 bears a single knob-like tubercle or large stumpy granule on the lateral wall at its union 

 with the abactinal area, and close to the aboral margin of the plate. The third and fourth 

 plates from the median interradial line also bear a similar tubercle close to their inner 

 margin, adjacent to the paxillar area ; and in one instance the fifth plate is similarly 

 furnished. The last three plates may bear one or two smaller granules near their aboral 

 margin, and the terminal plate may also bear from one to three granules at its 

 extremity. 



The infero-marginal plates are ten in number. They are similar in character to the 

 superior series, being smooth, and margined by a single series of bead-like granules ; and 

 they bear two or three knob-like granules near their aboral margin at the junction of the 

 actinal and lateral areas. On the plates at the base of the rays there is a tendency for 



