21 



which differ in their convexity, some having cuneiform spines on 

 the larger plates, and others having a plate here or there with a 

 sharp spine. We have examined specimens varying from an 

 eighth of an inch to an inch and a half in diameter, possessing, 

 in every rt spect, the same substantial characters. Occasionally 

 there is an increase in the number of plates, in the interradial or 

 azygous areas or on the vault, from the normal number, but the 

 radial plates and twelve ambulacral openings are features that 

 remain unchanged. 



Found in the Burlington Group, at Bui'lington, Iowa, and now 

 in the collection of Charles L. Faber, in whose honor the spe- 

 cific name is proposed. 



AMl'HORACRINUS JESSIE.!:, n. sp. "- 



Phde III, Fig. 18, azygous side, Ihe vault retains part of the 



matrix, hence the transverse truncation of the 



figure; Fig. 19, basal view. 



Species rather below medium size. Calyx bowl- shaped, some- 

 what broadly truncated or flattened below, and subpentagonal in 

 transverse section above, nearly twice as wide as high. Radial 

 ridges defined from the center of the first radial upward, and be- 

 coming stronger as the arms are approached. Plates convex and 

 more or less pyramidal. 



Basals form an hexagonal disc, with re-entering angles, about 

 one-third wider than the diameter of the column, which attached 

 in a moderately concave depression. First radials longer than 

 wide, and abruptly curve upward from the central, angular, com- 

 mencement of the radial ridges, three hexagonal, two heptagonal. 

 Second radials about two-thirds as large as the first, wider than 

 long, hexagonal. Third primary radials short, much smaller than 

 the second, pentagonal, axillary, and support on each upper slop- 

 ing side a single small secondary radial, which is axillary, and 

 supports upon each superior sloping side a free arm. The sec- 

 ondary radials and arms are directed nearly horizontally. There 

 are four arms to each ray, or twenty arms belonging to this 

 species. The arms are very small and round on the lower side. 



The interradial areas curve over upon the vault so as to leave 

 the radial series standing out prominently. There are three regu- 

 lar interradials in each area. The first one is larger than a sec- 



