48 FOSSIL ASTEROIDEA. 



Body rather small, or at most only of medium size. General form depressed. 

 Abactinal surface flat, or with a tendency for the rays to be slightly directed 

 upward at the extremities. Actinal surface slightly convex. Marginal contour 

 pentagonal, with the sides slightly lunate, though the curvature is often more or 

 less flattened; the extremity of the rays is only slightly produced. The major 

 radius measures about one-third more than the minor radius, the major dimension 

 being proportionately rather greater in large tests than in small ones. The 

 margin is thick, and the lateral wall has more of a precipitous than a rounded 

 character, although the infero-marginal plates are well rounded on the actinal 

 surface. 



The supero-marginal plates are three in number, counting from the median 

 interradial line to the extremity, or six from the tip of one ray to the tip of the 

 adjacent ray, exclusive of the odd terminal or " ocular " plate in each case. They 

 form a broad border to the abactinal area of the disk, of uniform breadth through- 

 out, which measures about 7 mm. at the median interradial line in an example 

 whose major radius measures 36'5 mm. and minor radius 27 mm. (PI. XIV, fig. 2 a). 

 Excepting the ultimate paired plates, the four intermediate supero-marginal plates on 

 each side of the disk are of equal size, the breadth being about once and a half the 

 length, the actual measurements in the specimen under notice being length 5 mm., 

 and breadth 7 mm. The abactinal surface of these plates is tumidly convex, while 

 the lateral wall is plane and vertical, and the abactinal tumidity commences 

 abruptly at a little distance from the adcentral margin of the plate, which leaves a 

 small level area at the rounded end of the plate abutting on the abactinal plates or 

 paxillar tabulas. On the surface of this level band near the adcentral margin, and 

 forming a more or less definite series running parallel to it, are three or four 

 irregular tubercular eminences or granules, but very indistinct and more or less 

 weatherworn (see PI. XIV, fig. 2 c). The entire margin of the plate is surrounded 

 by a very narrow depressed border, with very fine, closely crowded, uniserially 

 disposed punctations, upon which a small miliary granulation was previously borne. 

 The whole general superficies of the plate is smooth and weatherworn in every 

 example I have seen. The height of the plates as seen in the margin is as great 

 as or even slightly greater than their length, and the prominently tumid character 

 of the plates abactinally causes them to appear in the lateral view somewhat like 

 truncate cones abruptly rounded (see PI. XIV, fig. 2 b). 



The ultimate paired plate is larger and longer than any of the other plates, 

 and is of a diiferent and very peculiar shape. It is subtriangular in form as seen 

 from above, produced and pointed at the extremity, and to a certain extent recalls 

 the form of a ploughshare or coulter in consequence of a peculiar nipped-in 

 appearance caused by the extension of a tumid region which runs parallel to the 



