40 FOSSIL ASTEROIDEA. 



■covered with small subregular hexagonal plates or paxillar tabulae, which are, 

 however, comparatively large for the size of the species. The primary apical 

 plates are large and conspicuous, and all the plates in the central area of the disk 

 and in the interradial areas are considerably larger than elsewhere ; all diminish 

 in size as they approach the margin of the disk. All the plates have their surface 

 covered with a small, uniform, closely placed granulation, in which an indefinite 

 subcircular arrangement in relation to the centre of the plate is discernible (see 

 PI. XIII, fig. 2 d). 



The madreporiform body is small and subtriangular in outline ; its surface is 

 sculptured by fine striations which radiate from the centre to the margin. The 

 madreporite is usually enclosed by three plates, but four may be present in conse- 

 quence of the division or retarded development of one of them, as is the case in 

 the example figured on PI. XIII, fig. 2 c. The position of the madreporite is 

 rather nearer the centre of the disk than the margin. 



The infero-marginal plates are at least six in number, counting from the 

 median interradial line to the extremity, — that is to say, there are twelve (or 

 perhaps more) 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 equal to that of the superior series, but there are three 

 infero-marginal plates corresponding to the ultimate paired supero-marginal. As 

 seen in the lateral wall of the disk, the height of the infero-marginal plates is greater 

 than that of the supero-marginal series. The breadth of these plates, adjacent to 

 the median interradial line on the actinal surface, is 5 mm. in an example whose 

 minor radius measures about 15 mm. The breadth of the marginal border appears 

 to be well maintained till near the extremity. The surface of the plates is 

 ornamented in a similar manner to that of the supero-marginal plates, excepting 

 that the punctations on the main area are rather more numerous, and that the 

 finely punctate depressed border round the margin of the plate is much broader 

 than in the plates of the superior series ; the border is broader on the adcentral 

 margin of the plate than elsewhere. (Compare figs. 3 b and 4 h on PI. XIII.) 



The adambulacral plates appear to be comparatively small, but their preserva- 

 tion in the examples examined is not sufficiently good to permit of description. 



The actinal intermediate plates, which are small and hexagonal, are covered 

 with small, closely crowded, uniform granules. All are much displaced in the 

 specimens under notice. 



Dimensions. — In the example figured on PI. XIII, fig. 2 a, the major radius is 

 about 32 mm., and the minor radius about 25 mm. The length of the side is 38 

 mm. The thickness of the margin is about 8 mm. In Forbes's type (PI. XIII, 

 fig. 3 a) the major radius is about 20 mm., and the minor radius about 15'5 mm. ; 



