41 



The vault is only moderately elevated, but the radial ridges 

 are sharply elevated over the ambulacral canals. The azygous 

 orifipe is at the top of a central, short elevation. The plates 

 bear small nodes. The sutures between the plates are not dis 

 tinct in our specimen, and for that reason are not shown in 

 the illustrations. Ovarian apertures small and at the base of 

 the free arms. One on each side of each pair of arms or six- 

 teen in all. 



This species is distinguished from all other sixteen-armed 

 species by its general form and surface ornamentation, and 

 also by the plates in the interradial areas, and by the arm 

 formula. 



Found by J. F. Hammell in the H imiltoii Group, near Charles- 

 town, Indiana, and now in the collection of Win. F. E. Gurlcy. 



DOI.ATOCRTNUS PRECIOSUS, n. Sp. 



rUtfc II, Fig. 30, basal view; Fig. 31, summit view; Fig. 32, 

 vieiv upposile azygous area. 



Species above medium size and very handsomely ornamented. 

 Calyx broadly truncated at the base, and constricted below the 

 arms. Radial ridges delicate, with sharp elongated nodes at 

 the central part of the plates. Surface marked by radiating 

 lines of sharp nodes, which are longitudinal, in the upper part 

 of the interradial areas. In some cases the nodes coalesce so 

 as to form lines. The column is round and medium size. 



Basal plates form a hollow cone within the cavity of the 

 calyx, which is filled with the end of the column so as to 

 leave a pentagonal disc, at the surface, only a little wider than 

 the diameter of the column. First primary radials nearly as 

 long as wide and subequal in size. Second primary radials 

 large, quadrangular, and about as long as wide. Third primary 

 radials expand to the superior lateral angles. They are larger 

 than the second, pentagonal, axillary, and in the ray on the 

 right of the azygous area and in the left lateral ray, as seen 

 by looking at the vault, bear upon each upper sloping side a 

 single secondary radial, which is axillary and bears upon each 

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

 rays four arms. In the ray on the left of the azygous area, 

 and in the right lateral ray, the third primary radials bear 



—6. 



