428 THE CANADIAN NATURALIST. [Dec. 



the whole of the external integument seems to have been respira- 

 tory, as all, or nearly all, of the plates of which it is composed, 

 are more or less occupied by variously arranged, poriferous or 

 tubular structures. The Cystideans of these two groups hold 

 the lowest rank of all those known. In their general structure 

 they are mere sacks of a globular, ovate, or (as in the case of 

 Trochocystites) flattened form. Their test consists of an indefi- 

 nite number of plates without any radiated arrangement. They 

 were also, according to our present knowledge, the first to make 

 their appearance, two of the genera, Troclioajstites and Uoci/stitcs, 

 having been discovered in the primordial zone. No other echino- 

 derms have been found in rocks of so ancient a date. 



Next in order may be placed those genera whose test is com- 

 posed of a definite number of plates, which have, to some extent, 

 a quinary arrangement. Thus, Gli/ptocj/stites, EcJiinoencrinites, 

 Apiocystites, and several others, have each four series of calycine 

 plates, of which there are four plates in the basal and five in each 

 of the other three series. The respiratory areas or hydrospires 

 are reduced in number — ten to thirteen in Glyptocystites, and 

 three in most of the other genera of the group. Neither in the 

 plates nor in the hydrospires is there exhibited any tendency to a 

 radiated arrangement. The most ancient genus of this family is 

 Glyptocystites, which first appears in the Chazy limestone and 

 seems to have become extinct in the Trenton. The other genera 

 occur in various horizons between the Chazy and the Devonian. 



In the genera Hemicnsmitts and Caryocrinus the hydrospires 

 in the upper part of the test converge toward, but do not reach, 

 the central point of the apex, thus forming the commencement 

 of that concentration and complete radiation which is exhibited 

 in the ambulacral canal system of the higher echinoderms. In a 

 former note (this vol. p. 286,) it is pointed out that Caryocrinus 

 has thirty hydrospires, — ten at the base with their longer 

 diagonals vertical — a zone of six round the middle, with their 

 diagonals horizontal, and a third band of fourteen around the 

 upper part of the fossil. These latter are represented in fig. 1, 

 as if spread out on a plane surface. On consulting this figure it 

 will be seen that the flat tubes of the hydrospires, represented by 

 the parallel lines, all converge toward the central point from 

 which the dotted lines radiate. This point is the position of the 

 mouth in the recent echinoderms, but in Caryocrinus it is 

 occupied by a large solid imperforate plate. The hydrospires 



