ASTEROIDEA DREDGED DURING CRUISE OF H.M.S. "TRITON." 161 



Outward from each of the radial plates proceeds a longitudinal series of plates 

 which extends along the median dorsal line of the ray, each plate regular in 

 form (subhexagonal) and touching or slightly imbricating upon its next serial 

 companion. On either side of this median line of plates is a parallel line of 

 smaller plates, and these are succeeded by a line or series of plates nearly equal 

 in size to those of the median line ; the outer of these lines of plates standing 

 on the rounding which separates the dorsal and lateral areas of the ray. 

 Between this dorso-lateral line and the adambulacral plates are five longi- 

 tudinal and parallel series of plates, the three upper rows forming the sides of 

 the ray and the two lower being on the tumid actinal surface. The plates of 

 the two upper rows of the lateral series are broader than those in the three 

 lower series. The longitudinal arrangement of all the series is perfectly 

 regular, and the plates diminish gradually in size as they proceed outward. 

 Excepting the median dorsal line, the plates of all the other rows form regular 

 transverse series, as well as longitudinal. The plates of the median dorsal line 

 are slightly larger than the others, and consequently do not correspond. All 

 the plates are contiguous, but leave a small diamond-shaped or sub-circular 

 mesh between the rounded corners of adjoining plates. This is covered with 

 membrane, through which one or more small papulae proceed, and on which are 

 usually borne one, or occasionally two, small forficiform pedicellarise. The 

 meshes form perfectly regular longitudinal lines, and this character, as well as 

 their presence, is rendered more conspicuous by the slightly tumid surface of 

 the plates. The surface of all the plates is studded with a number of small, 

 uniform, well-spaced miliary granules, on which are articulated very short 

 ciliary spinelets thinly covered with membrane. The plates of the median 

 dorsal line are sub-mammillated, rising to a small but definite tubercle in the 

 middle, which gives attachment to a short, robust, conical spinelet, the sur- 

 rounding portions of the plate being covered with the same small miliary 

 granules and spinelets as the other plates. Isolated dorso-lateral plates are 

 occasionally similarly mammilated and spined, and the large interradial plates 

 on the disk are also usually thus furnished. On the plates of the three rows 

 which succeed the adambulacral plates, there are usually one to three spinelets 

 much longer and more robust than the accompanying miliary spinelets. These 

 are naked, delicate, cylindrical, and taper to a fine extremity, and are generallv 

 arranged in slightly oblique lines, with the middle spine often more forward 

 and longest when three are present, near the lower margin of the plate, and 

 they are directed upward and appressed to the ray. The next row on the sides 

 of the ray, i.e., the fourth from the adambulacral plates, has one larger spine on 

 each plate, of equal size to the afore-mentioned. The adambulacral plates are 

 quite within the furrow, and are short but broad, extending far upward almost 

 vertically. Each alternate plate is developed into a thin prominent ridge, 



VOL. XXXII. PART I. 2D 



