1865.] BILLINGS — SILURIAN AND DEVONIAN FOSSILS. 197 



one side (the flattened side) of a specimen in the cabinet of Dr. J. 

 A. Grant, of Ottawa, there is a small elevation which may have 

 been the point of attachment. No orifices have yet been made out, 

 but it must be observed that no specimen has been collected in 

 which the whole of the surface can be examined. None that I 

 have seen have a vestige of the integument remaining. The plates 

 (or rather their impressions) are, in these specimens, for the greater 

 part, strongly convex and precisely like those of P. Ilalli, only 

 larger. In some they are partly concave and partly convex or flat. 

 Individuals also occur which have them either convex, all flat, or 

 all concave. Yet as these occur together in the same localities, I 

 think them all one species. They have, as yet, been found only 

 at the city of Ottawa in the Trenton limestone. 



In one piece of shale scarcely a yard square, I collected about 

 fifty individuals, but although they occur thus abundantly in cer- 

 tain spots, good specimens are exceedingly rare. 



This genus was first described by me in the Report of the 

 Geological Survey of Canada for 1857, p. 342, and placed among 

 the fossils of uncertain class. The two species above figured are 

 also there described. They have been on exhibition in the cases 

 of our museum for the last ten years, and have been examined by 

 a great many of the naturalists of all countries. But I do ot 

 think we yet know to what class they belong. P. Halli and 

 Ischaditcs Canadensis are figured on p. 304, of the Geology of 

 Canada, as members of the Tunicata. The latter, however, is a 

 true Receptaculites. It is barely possible that the former may be 

 a tunicate, but we have no positive evidence that it is. 



Eichwald, in his Lethaea Rossica, has described and figured two 

 species, Cyclocrinus Spaskii and C. exilis, which appear to me to 

 be either congeneric with our two, or, at least, to belong to the 

 same family. Both of Eichwald's species are small globular 

 bodies covered with hexagonal or pentagonal plates. The plates 

 of C. Spaskii have a tubercle in the centre and a number of 

 obscure rounded ridges radiating to the sides. He says there is a 

 small oral orifice on one side, and on the side opposite, a rudimen- 

 tary pedicle. One of his figured specimens is covered with a tubular 

 incrustation consisting of small cells which he considers to be a 

 part of the integument itself. It may be, however, a coral. A 

 fragment of one of the specimens of P. Halli from Anticosti is 

 incrusted in precisely the same manner with what I take to be a 

 species of Stenopora. Eichwald places his genus among the 



