METO PASTE 11 MANTELLI. 3» 



there would appear to be only seven plates on the entire side, but only one 

 radial angle is preserved intact, and much displacement of plates has occurred. 

 The circumstance is in any case of comparatively trifling importance. The 

 supero-marginal plates form a conspicuous and moderately broad border to the 

 abactinal area of the disk, of uniform breadth throughout, and measuring about 

 6 mm. at the median interradial line in an example whose minor radius measures 

 about 25 mm. 



Excepting the ultimate paired plate all the supero-marginal plates are nearly 

 subequal in size ; the plates, however, adjacent to the median interradial line are 

 slightly longer in relation to their breadth than those adjacent to the ultimate 

 paired plate. The plates adjacent to the median interradial line have the appear- 

 ance of being nearly square in outline as seen from above, the actual dimensions 

 in the specimen under notice, whose side measures 38 mm., being length 5 mm., 

 and breadth (> mm. In a smaller example, with a side measurement of 29'5 mm., 

 the corresponding plate is 3"5 mm. long and 45 mm. broad. In Forbes's type 

 the measurements are, length 3-75 mm., and breadth 5 mm. 



The abactinal surface of the supero-marginal plates is slightly tumid, and the 

 general surface of the whole series forms a well-rounded regular curve from the 

 adcentral margin to the margin in the lateral wall adjacent to the infero-marginal 

 plates. The height of the plates as seen in the margin is less than their length, 

 the actual measurement being about 3 mm. Their abactinal contour is distinctly 

 convex, but not gibbous. The whole superficies of the plates is covered with 

 small, widely spaced, equidistant, uniform punctations. In some examples which 

 have been subjected to much weathering the punctations are almost obliterated, 

 as in the case of the fine specimen shown on PI. XIII, fig. 2 a. A narrow 

 depressed border surrounds the margin of the plate, bearing very small, closely 

 crowded punctations, those adjacent to the main or median area being in serial 

 arrangement. Occasionally a small entrenched pedicellaria may be detected on 

 the median area of the plate (see PI. XIII, fig. 2 b). 



The ultimate paired plate is small and triangular in outline as seen from above, 

 and one margin touches the corresponding plate of the adjacent side of the disk 

 throughout, the junction coinciding with the median radial line of the disk. The 

 length of the plate — that is to say, of the side of the plate which falls in the margin 

 of the disk — is a trifle greater than the length of the largest supero-marginal 

 plate, measuring in the example under notice nearly 5*5 mm., whereas the 

 breadth of the plate, or measurement of the side adjacent to the penultimate 

 supero-marginal plate, is not more than 5 mm. Near the outer or apical extremity 

 of this plate when seen from above there is frequently a more or less strongly 

 developed tendency to gibbo.sity present. 



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



