52 



this arrangement the basal plates, when united, form a 

 disc having eleven sides and abuts upon eight, plates, a pecu 

 liarity we have never observed in any other fossil. 



The first primary radials are longer than wide, very un- 

 equal in size, two pentagonal, two hexagonal, and one heptag- 

 onal. The radial series are so different that we will describe 

 them separately. The first primary radial that truncates the 

 pentagonal basal plate is the largest plate in the body, heptag- 

 onal, and has a width greater than its length. It is followed 

 by a second primary radial, one-half smaller than the first, 

 longer than wide and heptagonal. This is followed by a short, 

 small, third primary radial that is heptagonal, axillary and 

 supports upon each superior sloping side a small secondary 

 radial, which gives to this ray two arm openings that enter 

 the vault horizontally. In one of the series, supported in one 

 of the re-entering angles of the basal disc, the first primary 

 radial is very large and hexagonal. It is followed by a second 

 primary radial, that is very large, wider than long, heptagonal, 

 axillary, and supports on one of the superior sides a single, 

 secondary radial, which is axillary and supports tertiary radials, 

 and upon the other two secondary radials, the last of which is 

 axillary and supports tertiary radials, which gives to this ray 

 four arm openings to the vault, that are directed horizontally. 

 In the other series supported in a re-entering angle of the basal 

 disc, the first primary radial is much smaller than the one 

 last described, longer than wide and pentagonal. It is followed 

 by a second primary radial much larger than itself, wider than 

 long, having eight sides, axillary and supporting, on the left 

 lateral side a single secondary radial that is axillary and supports 

 tertiary radials, and, on the superior side, a single secondary 

 radial that is not axillary, and, on the right lateral side, a 

 secondary radial that is axillary and supports tertiary radials, 

 which arrangement gives to this ray five arms. It will be 

 noticed here, that the two radial series supported in the re- 

 entering angles of the basal dis3 have no third primary radials. 

 In the radial series, on the right of the azygous area, the first 

 primary radial is large, longer than wide, hexagonal, and 

 followed by a second primary radial, which is much smaller, 

 hexagonal, and followed by a third primary radial, which is 



