﻿5§ SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 47 



between them, but interrupted at the suture lines between the plates 

 (pi. xv, fig-. 2b). 



Basals three, the suture lines between them distinctly visible. 

 The form, size, and relative position of the plates of a nearly com- 

 plete individual are shown by the accompanying diagram (fig. i). 

 Arms sixteen, four in the anterior and postero-lateral rays, and two 

 in each antero-lateral ray. A ray with four arms has usually one 

 interdistichal, followed by two interpalmars placed side by side, but 



•°«%& 







Fig. i. — Megistocrinus tuberatus n. sp. Arrangement of calyx plates. 



the number of these plates is not constant. The number of inter- 

 brachial plates beyond the second row is also variable, but there are 

 commonly three plates in the third row with two in each succeed- 

 ing row. The anal plate is similar in size and surface ornament to 

 the radials. It is followed by three large plates in the second and 

 four in the third row. Plates of the succeeding rows vary in num- 

 ber in different specimens, and are irregular in arrangement. 



'fhe tegmen is moderately convex, and but slightly depressed be- 

 tween the arm bases. It is formed of thick plates, large near the 

 en iter, but small and very numerous toward the arm regions. The 

 posterior oral is large and strongly spinose ; the other orals are 

 gently convex and but little larger than the neighboring plates of 

 the tegmen. The radial dome plates bear stout spines. Anal tube 

 subcentral. 



Column circular in section, with large pentalobate canal. 



