54 FOSSIL ASTEROIDEA. 



merges in the rounding of the high lateral wall of the plate. On the level area 

 o£ the plate, which is consequently the inner or adcentral part of the surface, are 

 several low tubercular eminences of irregular shape and disposition, but which 

 appear to assume a more or less distinct biserial arrangement at right angles to 

 the adcentral margin of the plate. They appear to be enlarged irregular granules, 

 and in all the examples I have examined they have become to a certain extent 

 ill-defined, owing either to growth or to weather-wearing. The general character 

 of the ornamentation is shown in PL XIV, fig. 4 c. The entire margin of the 

 plate is surrounded by a very narrow depressed border, which is very minutely 

 punctate, probably only in a single lineal series. The general superficies of the 

 plate beyond the ornamentation mentioned is smooth, as if weatherworn, in all 

 the examples I have seen, but in some specimens there appear to be traces of a 

 more or less granulous character, and in some instances suggest the impression 

 that an ornamentation similar to that noticed in Mitraster rugatus was probably 

 present on at least a part of the surface of the plate. The height of the supero- 

 marginal plates as seen in the margin is greater than their length, and their 

 prominent abactinal tumidity has a distinctly conical character from this point 

 of view. 



The ultimate paired plate is fully twice as long as the other supero- marginal 

 plates measured on the outer margin, and its breadth is equal to that of the 

 adjacent supero-marginal. It is triangular in form, and the line of junction with 

 the companion ultimate plate of the adjacent side coincides with the median 

 radial line. The actual dimensions in the example under description are, length 

 6'2 mm., breadth about 6 mm. As seen in the lateral view of the disk the 

 ultimate plates are distinctly tumid abactinally (see PI. XIV, fig. 4 6). The 

 abactinal surface of the plate is ornamented by a number of miliary tubercles or 

 granules, more or less serially disposed parallel to the margin adjacent to the 

 companion plate, and more numerous at the adcentral end of that margin. 

 Beyond this the surface of the ultimate plate is smooth, like that of the other 

 supero-marginal plates. 



The abactinal area of the disk within the boundary of the marginal plates is 

 covered with hexagonal or polygonal plates or paxillar tabulas, which are small in 

 size generally, excepting the primary apical plates, which are comparatively very 

 large. All the plates have their surface covered with a fine, uniform granulation. 

 The primary apical plates have a small central area of low elevation, not higher 

 than if a number of granules had become coalesced — the structure being sugges- 

 tive of a tubercle in process of disappearance, — in other words, the scar left by a 

 tubercle which had existed in an earlier stage of growth (see PI. XIV, fig. 4(Z). 



Dimensions. — The example figured on PI. XIV, fig. 4 a, has the following 



