﻿New Genus aiid Species of Cystideans. 289 



exclusively occupied with five large linear lanceolate, 

 radiating ambulacral areas, which extend a little beyond 

 and below the midheight and alternate, at and near 

 the centre, with five small narrowly elongated, sub- 

 triangular, almost bottle-shaped plates. The ambulacral 

 areas consist of well defined grooves, which are partially 

 and perhaps in perfect specimens were wholly roofed over 

 with two rows of small, transversely elongated and 

 alternately arranged covering plates, from the centre of 

 the summit, where they interlock and probably cover 

 the presumably subtegminal mouth. In the only speci- 

 mens known to the writer these plates roof over the 

 ambulacral grooves, from the middle of the summit, 

 for distances varying from one-half to fully two-thirds 

 of the entire length of each groove, but always, at 

 least, as far outward as to the bases of the small 

 alternating subtriangular plates. On some of the 

 ambulacral grooves only eight covering plates can be 

 counted on each side, in a longitudinal direction, but on 

 others there are as many as fourteen on each side. 

 In the latter case the circumstance that several of 

 the outermost covering plates are crushed down into the 

 ambulacral grooves leads to the inference that the grooves 

 may have been almost or completely roofed over in perfect 

 specimens. A central area at the summit, in which 

 the ambulacral areas or covered inner ends of the 

 ambulacral grooves are everywhere in close contact with 

 the small alternating subtriangular plates, is bounded 

 by the bases of the latter. Outside of this area the 

 ambulacral areas suddenly become more widely divergent, 

 and their grooves are bordered on each side by a 

 prominent raised rim. At the outer end of each of the 

 ambulacral areas, where the covering plates have been 

 removed or are absent, there is a longitudinal row of 

 marginal pores on the inner surface of the raised rim 

 which bounds the crroove on both sides, as shewn in 



