12 



somewhat flattened and elischtly depressed ; plates thin ; surface 

 ornamented with low radial ridges, which commence on the first 

 radial and extend to the tei'tiarv radials, and witli short radi- 

 ating ridges from tlie center of each j)late to eaeli adjoining 

 plate, while the interradials bear a central node with a low radi- 

 ating ridge to each adjoining plate. Dome conical and slowly 

 diminishing into a largo ventral tube composed of tumid and 

 strongly protuberant plates. 



Basals three, pentagonal, about as large as the first radials, 

 and forming a cup, half as high as wide, slightly constricted in 

 the middle, so as to form a rounded rim, on the lower half, tliat 

 projects a little beyond a rather large column; surface smooth, 

 not sculptured. 



First primary radials large, length and breadth subequal, hex- 

 agonal and heptagonal. Second primary radials about half as 

 large as the first, hexagonal and having the superior sloping 

 sides -shorter than the inferior sloping sides, (Fig. 8 is not ex- 

 actly correct, in this respect, the artist having followed an ink 

 Hue instead of the suture). Third primary radials smaller than 

 the second, heptagonal and bearing upon each upper sloping 

 side a single secondary radial. Each secondary radial supports 

 on each upper sloping side three or four tertiary radials, one 

 of which in each series is axillary on the third plate, from which 

 two arms arise, which gives six arms to each radial series, so 

 far as they are preserved in tlie two specimens illustrated, by 

 figs. 8 and 8 a, or thirty arms in the species. The arms are 

 composed of a double series of interlocking plates and thej fre- 

 quently bifurcate. One tertiary series illustrated in fig. 8 a shows 

 eight arms witliin an inch of the calyx, and if the other arms 

 bifurcate in like manner, tliere are eighty arms within an inch 

 of the calyx, and, judging from appearances, there are numerous 

 bifurcations above those sliown in the specimen. 



First interradial hexagonal, smaller than a second primary 

 radial, followed by two smaller plates, in the second series, three 

 smaller ones in the third series, and three smaller ones in the 

 foui'th scries, tliat unite with the plates of the vault. 



The first azygous plate is smaller than a first primary radial, 

 it is followed by two plates in the second series, three in the 

 third, and four in the fourth, above which the plates are not 

 determined. 



