32 



ASTEROIDEA. 



long, slender, and simple, and form a pentagonal rosette in the centre of the disc ; they 

 are constructed of two rows of alternating quadrate ossicles, which have their outer margin 

 indented superiorly, to form spinigerous crests. The spines are apparently short, and not 

 equal in length to that of an ossicle, obtuse, and few in a row. The raadreporiform plate 

 (fig. 1 8, « ) has been found between two of the rays. This remarkable genus reminds us, 

 at first sight, of tlie OpMuridce, to which it was referred by its author. The discovery of the 

 madreporiform plate, however, removes it to its place among the Asteriada. The alternating 

 quadrate ossicula of the arms connect it by osteological affinities with the Euryalida, of 

 which it appears to have been the ancient type. 



Proiaster Miltoni, Salter. Ann. and Mag. of Nat. Hist., 2d. series, vol. xx, p. 330, pi. 



ix, fig. 4. 



Fig 



"Disc round, one inch in diameter, and covered with small ridged plates; the 

 arms are wide, composed of large ossicles, which become smaller at their base of insertion 



in the disc above, having a wedge- 

 shaped space between, which, joined 

 with those of the other arms, forms 

 a conspicuous pentagon above, equal 

 in size to that formed by the di- 

 vergent ossicles of the mouth below. 



The arms themselves are made 

 up of a double row of about forty 

 pairs of squarish concave plates above, 

 placed exactly opposite, not alter- 

 nating as in other species (fig. 18 

 The sutures between these are deep^ 

 and the inner angles marked with a 

 deep pit or pore, bounded by tubercles, set cross-fashion. The outer margin bears a tuft of 

 spines, long and short. On the under surface (fig. 18, c) the marginal plates are highly 

 convex, and between them lies a double row of central plates of an hour-glass shape, on the 

 outer sides of which, and between them and the marginal row, is a large, round aperture 

 on either side — the passage for the tubular feet. The marginal plates bear a row of spines 

 as long as the width of the arm, and striated across (fig. 18, c). 



The oral pentagon is made up of twenty bones, five pairs of which are the central row 

 enlarged (fig. 18, b), and these diverge at a wide angle, and nearly join the neighbouring 

 pairs ; the other five belong to the lateral rows, and are linear, set parallel, and bear the 

 conspicuous, triturating combs of spines. The oral ossicles in this species form an angular 



Protaster Miltoni, Salter. 



b. The upper surface of a ray. 



c. The under surface of a ray with the oral combs. 



