318 



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 jalter- 

 nating subtriangular plates, is bounded by the bases of the latter. Out- 

 side 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 groove on both sides, as shewn in fig. 22, and the whole of the outer 

 declivity or downward slope of the rim is transversely corrugated or 

 ribbed. 



" When examined with a lens, the whole surface of the calyx, of the 

 covering plates of the ambulacral grooves and of the small subtriangular 

 plates which alternate with the inner ends of the ambulacral areas at the 

 summit, is seen to be densely pitted or perhaps perforated. 



" Two specimens of this species, both collected by Mr. John Stewart in 

 1886 from the Trenton limestone at Division St., Ottawa, are in the 

 Museum of the Geological Survey of Canada, and an imperfect specimen 

 from the same locality has been kindly lent to the writer by Mr. Walter 

 B. Billings. All three of these specimens, when found, were almost com- 

 pletely covered with a very tenacious shaly limestone, and although they 

 have been both carefully and skillfully cleaned, it is just possible that 

 some of the covering plates of the ambulacral grooves may have been acci- 

 dentally removed in the cleaning. At present, also, it is not possible to 

 ascertain from either, whether the dense pitting of so large a portion of 

 their surface is caused by " conjugate " pores or not. It is only proper to 

 add that the general outlines of the plates of which the calyx is composed 

 in this species, were first suggested to the writer by Mr. W. R. Billings, 

 who, as is well known, has devoted much time .to the study of the crin- 

 oids and cystideans of the Trenton limestone of the Ottawa valley. 



" Astrocystites would seem to be most nearly related to Asterohlastus, 

 Eichwald, and is probably referable to the same family, though it clearly 

 difiers from that genus in several important particulars. Thus, a compari- 

 son of the plates of which the calyx is composed in these two genera 

 shews that, although they have much the same shape and style of sculp- 

 ture, yet those of Asterohlastus are both small and very numerous, while 

 those of Astrocystites are large and comparatively few in number. The anal 

 region of Astrocystites, too, is lateral and well defined, but no indications of 



