IIG s. GrOTO: 



are xeij fine and small, and are made np of about five to ten spinelets. 

 Towards the margin tlioy become smaller, and also in the centre, where thej' 

 are very compact — a slightly prominent peak being formed as in Ctenodisctts. 

 A slight elevation of the sin"face is present in the median radial Hne, opposite 

 the base of each ray, and at about one-tliird of the distance from the margin 



to the centre. 



" The marginal plates occupy the entire lateral region, and represent 

 the whole thickness of the animal, forming perj^endicular walls regularly 

 roimded above and below. Along the rays, the supero-marginal plates meet 

 in the median radial line, and form a complete casing to the ray, wliicli is 

 well roimded, small, and tapers but slightly. The supero-marginal plates are 

 eight in number (or, coimting a very small aborted one, nine), exclusive of 

 the terminal. The i)lates wliich fall in the margin of the disk i^roper have 

 the length about equal to their height, but in those along the ray the height 

 is greater than the length. 



" The infero-marginal j)lates correspond in number and in length to the 

 superior series. In the interbracliial arc, along the disk proper, the height 

 is about equal to the length, and the plates are uniform in size with the 

 superior series. Towards the extremity of the ray the height diminishes 

 gi-adually, and the length is gi-eater than the height — a reversal of the 

 relative propoi-tions presented by the plates of the superior series. The 

 marginal plates are smooth and bear no spines; but when examined 

 microscopically have the appearance of being subgi-anular, and built up of 

 a rather open network. The i^lates of both series are convex outwardly 

 or tumid in a veiy slight degi-ee, by which means the sutm-al divisions- 

 of the segments are clearly marked out, and a somewhat annulated 

 appearance is given to the ray. The terminal plate is large and con- 

 spicuous, appearing somewhat tubercular when viewed in profile, and oval 

 in contour when seen from above. This plate bears tln-ee short and rather 

 robust spinelets — one at the terminal extremity of the plate, situa'-ed 

 in the median radial line, pointing in the direction of the prolongation 

 of the ray, and diverging but little from the horizontal. Below tliis spine, 

 and at each side of it, on the angle formed by the actual edge of the 



