46 FOSSIL ASTEROIDEA. 



rupted regular curve between the adcentral margin of the plate and the margin 

 in the lateral wall adjacent to the infero-marginal plates. The height of the 

 plates as seen in the lateral view of the disk is greater than their length, and 

 there is an apparent increase in height as the plates approach the extremity of 

 the ray, the ultimate plate being still higher and distinctly tumid (see PI. XII, 

 fig. 2 b). The whole superficies of the plates is covered with small, widely spaced, 

 equidistant, uniform punctations ; and there is a narrow depressed border sur- 

 rounding the margin of the plate with much smaller and closely crowded puncta- 

 tions, upon which minute miliary granules were previously borne. 



The ultimate paired plate is much larger than any of the other supero-marginal 

 plates, its length as measured on the outer margin being more than twice the 

 length of the other supero-marginal plates. Its breadth is about equal to that of 

 the adjacent supero-marginal plate. It is subtriangular in form as seen from 

 above, and the line of junction with the corresponding companion plate of the 

 adjacent side of the disk is complete throughout, and coincides with the median 

 radial line. The convexity of the plate falls in a line parallel and adjacent to this 

 margin of the plate, and its height is greatest there. From this convexity the 

 surface slopes gradually and regularly in conformity to the curve of the superficies 

 of the other supero-marginal plates. The actual dimensions of the ultimate plate 

 in the example under notice are, length 7 mm., breadth 7 ram. ; greatest height as 

 seen in the marginal view, about 8"5 mm. The surface of the ultimate plate is marked 

 with a precisely similar ornamentation to that on the other supero-marginal plates. 



The odd terminal plate is very small, and though only traces are present in 

 the type it is well preserved in other examples. It is prominent, cylindrical, and 

 abruptly truncate, resembling in all respects the form described in Metopaster 

 Parl'bisoni. 



The madreporiform body, which is only partially exposed in the example under 

 notice, is apparently subtriangular in outline, and is marked with very fine centri- 

 fugally radiating striations (see PI. XII, fig. 2 c). 



The infero-marginal plates ai'e seven in number, counting from the median 

 interradial line to the extremity, — that is to say, there are fourteen for the whole 

 side of the disk, as against eight in the supero-marginal series. The length of the 

 three innermost plates on each side of the median interradial line is subequal to 

 that of the superior series, but their height as seen in the marginal view of the 

 disk is much greater, the thickness of the whole margin, i. e. both series of plates 

 together, being 10 mm. in an example whose minor radius is 19 mm. Four plates 

 underlie the superior ultimate plate, the last two being very small and triangular 

 in form. All the four are adjacent to the adambulacral series of plates. The 

 ornamentation or surface-marking of the infero-marginal plates is precisely 

 similar to that of the supero-marginal series. 



