902 



DR. F. A. BATHER UN 



bands of lighter colour that accompany them (PI. XC. fig. 3). 

 The measurements in millimetres are : — 



The greatest width of each basal is on a level with its umbo, 

 at a little more than half its height. The umbo is most 

 prominent in the posterior basal, which is also the widest of the 

 basals and would be the highest were it not truncated by the 

 periproct. 



Radials sloping from top of basals to the peristome rather 

 suddenly. Height of each from the lower angle to the inner 

 mai'gin of the peristome about 8 mm. Width of each below 

 about 8'3 mm. ; width above about 2 mm. 



The upper margins of the radials form a distinctly pentagonal 

 border to the dorsal cup (PI. XO. figs. 1, 2). Each side of the 

 pentagon fonns a smooth slightly raised I'im, and is about 2"3 mm. 

 long. At each angle of the pentagon lies a brachial facet. 



Facets rather worn, so that their precise constitution cannot 

 be detected. A ventral groove leads downwards into the cavity 

 of the cup. Fiom this to the outer edge of the facet is about 

 rS mm. Width of facet about 1*3 mm. Neither muscle- fossee 

 nor an axial nerve-canal can be detected. 



Within the pentagonal rim, the edges of the radials slope 

 steeply downwards into the cavity of the cup {cf. PI. XC. fig. 5). 

 The downward extension appears to be greater near the facets 

 than near the interradial sutures, and may have served for the 

 attachment of muscles. There is no trace of any tegminal or 

 oral plates, or of any sutural surface on which they might have 

 abutted. This fact and the contraction of the cup at its upper 

 end lead one to regard the pentagonal opening as a peristome, 

 covered in life only by oral folds of a flexible and thinly-plated 

 or naked integument. Below the left posterior facet, in the 

 peristomial cavity, is a fragment of a j)late, but its nature is not 

 clear. 



The Periproct (PI. XC. fig. 1) truncates the uppermost angle 

 of the posterior basal with an obtuse re-entrant angle, 2"8 mm. 

 across, and cuts into the adjacent lower angles of the right and 

 left posterior radials with a curve of approximately the same 

 chord (2*8 mm.), also somewhat angular, so that the outline 

 is approximately an iiregulai' hexagon neaily 3 mm. high. Of 



