1908 546 F. A. Bather— Studies in Edrioasteroidea. 



to be composed of a double row of flooring-plates, alternately arranged. 

 These are rounded, and have in places a slight appearance of over- 

 lapping by their proximal margins. In the proximal region of a 

 groove, the long axis of any one of these plates is directed almost at 

 a right angle to the median line of the groove, but tends in a distal 

 direction; its length is 1*6 to 2 mm. ; the breadth of such a plate is 

 •9 to 1mm. There are from 21 to 25 plates along each side of 

 a groove : the lower numbers are on the adjacent sides of the right 

 and left pair. The greatest number is on the adanal side of the left 

 posterior ray. 



Each of these plates is excavated on its sides, but more on the side 

 towards the distal end of the ray (Fig. 2), so that the adjacent excava- 

 tions form a pore, which lies about half-way between the middle line and 

 the outer margin of the whole ray. The actual food-groove was very 

 narrow, and appears to have been covered with irregular plates, some 

 of which are preserved in places (Fig. 1). These covering-plates, 

 though small in proportion to the whole structure, are large compared 

 with the food-groove and do not seem to have had a regular alternating 

 arrangement. As to their existence, I have no doubt ; but the state 

 of preservation of the fossil forbids a more accurate account. 



The actinal centre is roofed over by relatively large irregular plates, 

 one or two of which are broken away on the right side, so that one 

 gets a suggestion of the underlying hollow, or vestibule of the mouth. 

 These covering-plates appear to be serially homologous with those of 

 the grooves, and their relations to them and to the flooring-plates are 

 best seen in the right posterior ray. 



The Interradial Areas are bounded by the flooring-plates of the 

 grooves and by the periphery, but were not separated by any 

 differentiated area from the under surface. They are covered with 

 relatively large and apparently thick plates of irregular shape. The 

 adoral margin of each plate slightly overlaps the adjoining margin of 

 the adjacent plate. This gives the effect of a slight adoral imbrication, 

 more perceptible the nearer the periphery. The plates become a 

 trifle smaller towards the periphery, but there is no sudden diminution 

 of size, and no break in their continuity with the peripheral plates of 

 the under surface. The plates are rugose, but it is hard to determine 

 precisely how far this is due to original ornament. At about half- 

 way between the actinal centre and the periphery the width of the 

 right posterior area is 5*4 mm., that of the posterior area 8*5 mm. 

 The distance from the distal extremity of the left posterior ray to that 

 of the right posterior ray is 15-1 mm., to that of the left anterior is 

 13 6 mm. The distance between the distal extremities seems to have 

 been a little less than 13-6 mm. in the other interradii, but exact 

 measurements are not obtainable. 



The conspicuously greater width of the posterior interradius is due 

 to the presence of the Anal Opening, clearly recognisable as such. 

 Its centre is 6*5 mm. from the actinal centre, and nearly on the middle 

 line of the interradial area. The plates of the valvular pyramid, if 

 they ever existed, have disappeared. The opening which remains is 

 surrounded by a border of plates smaller than the others of the same 

 area, into which they merge, and slightly raised above them, but not 



