82 THE CANADIAN NATURALIST. [Vol. X. 



The plates or pieces of which the calyx is composed are : three 

 basals, five radials, six inter-radials, one anal, several anteambu- 

 lacrals and numerous pseudambulacrals. In Pentremites, in which 

 the lateral opening is completely wanting, there is, of course, no 

 anal plate, and there are only five inter-radial or deltoid plates 

 present. The three basal plates of N. lucina (?) pass outwards 

 from the centre of the topmost joint of the slender pedicle, are 

 very small, irregular in shape, and almost altogether hidden by 

 the stem. Above these are the five dorsally-ridged radial plates 

 slightly forked upon their upper margins for the reception of the 

 lower extremities of the five pseudambulacral areas. These five 

 pseudambulacral fields with the five alternating interambulacral 

 areas form the sides of the calyx. Each pseudambulacral area 

 is much less " petaloid " in outline than the corresponding area 

 of Pentremites, being greatly lengthened and comparatively nar- 

 row throughout, and terminate below in a deep pit or depression 

 where the forked radial is raised into an arched eminence. The 

 centre of the area is occupied by a longitudinal furrow, which 

 with its two raised borders forms a long -And extremely narrow 

 lancet-plate. Outside the elevated ridges that bound this central 

 furrow on each side is a row of plates or tables numbering about 

 forty, perforated by minute but very visible apertures and known 

 as pore-plates. The remainder or outer portion of the pseudam- 

 bulacral area is believed to be made up of numerous transverse 

 plates because of its surface shewing very many small yet distinct 

 transverse grooves and elevations. These transversely-striated 

 lateral portions constitute the greater part of the area, and, in- 

 stead of gradually rising from the pore-plates and central lancet- 

 plate, gradually slope towards the outer edges, so that the whole 

 pseudambulacrum is strongly elevated towards and about the 

 middle line and depressed at its outer margins, as seen in Figure 

 1, a condition exactly the reverse of that which exists in Pen- 

 tremites (Fig. 2). 



Four of the interambulacral areas consist each of a single, long, 

 narrow, triangular or deltoid plate termed the "inter-radial," its 

 apex reaching the top of the calyx, and its base resting upon 

 two radials beneath. The fifth interambulacral area, however, 

 differs greatly from the others in being much broader (nearly 

 twice as broad), in the possession of a distinct and comparatively 

 large, circular opening near its summit, two deltoid or inter- 

 radial plates separated by a long, triangular and externally con 



