31 



long as wide, three hexagonal, two heptagonal. Second 

 primary radials about two- thirds the size of the first, hexagonal, 

 and nearly as long as wide. Third primary radials almost as 

 large as the second, hexagonal, axillary, and support on each 

 upper sloping side a single secondary radial, which is axillary, 

 and, in two of the rays, one of which adjoins the azygous 

 area, and the other a lateral ray on the same side, bears upon 

 each proximal side a single tertiary radial and upon each 

 distal side two tertiary radials, which gives to each of these 

 rays four arms. In the other three rays the distal side of 

 each secondary radial bears two tertiary radials and the 

 proximal side bears a single tertiary radial which is axillary 

 and bears upon each superior sloping side a quaternary radial, 

 which gives to each of these rays six arms. There are, there- 

 fore, twenty-six arms in this species. 



There are, in each of four of the regular interradial areas, 

 seven plates, one in the first range, two in the second, two in 

 the third, and two in the fourth. In the other area there are 

 eight plates. The last four plates are very small. In the azy- 

 gous area there are eleven plates. The first one is in line with 

 the first primary radials and about the same size. It is fol- 

 lowed by two plates, in the second range, three, in the third, 

 three, in the fourth, and above these, there are two very small 

 plates. The three plates, in the fourth range, are much smaller 

 than those in the third range. There are no inter-secondary 

 plates. 



Vault -moderately convex, composed of numerous convex, 

 polygonal plates, and bears a small nearly central proboscis. 



In describing this genus Meek & Worthen (5 111., 347,) in- 

 cluded as typical 8. perumbrosus and S. liraius and showed 

 that they had the structure of Aciinocrhius, ''Up to the divi- 

 sion of the rays, but with the body comparatively long and 

 narrow below, and the secondary and other succeeding sup- 

 plementary radials, brachial and intermediate pieces, connected 

 laterally all around, and spreading out horizontally far beyond 

 the limits of the body so as to form, with the flat or much 

 depressed vault, a broad, more or less distinctly ten-angled 

 disc, from the margins of which the numerous long, slender 

 arms arise, without bifurcating after becoming free.'' It will 

 be seen that this arrangement cuts off the interradial areas 

 from the vault and presents a structure of the calyx above the 

 third radials fundamentally different from that of Aclinocrinus. 

 They said further that; 



