28 NATURAL HISTORY BULLETIN 



In addition to these the lateral and interactinal plates have 

 one slender, articulated spine. 



The dorso-lateral row of plates next the carinal row is differ- 

 entiated, the plates being larger than the others and similar to 

 the carinals. The rest of the lateral and interactinal plates are 

 all similar, forming six to eight regular rows, imbricated both 

 longitudinally and transversely, leaving only small papular pores 

 between them. Marginals are not much different from the rest. 



Adambulacral plates of two sorts are very unlike. The larger 

 carry four to six divergent slender spines, along the thin carinate 

 edge ; the larger one at the margin of the groove may bear one or 

 several major pedicellarige, often large; other spines may bear 

 smaller ones. The much smaller alternate plates are not carinate 

 and bear usually two slender outer spines and a small one in the 

 furrow. Major pedicellari^ are scattered on the back and sides. 



Zoroaster ackleyi Perrier. 



Zoroaster ackleyi Perrier, Comptes rendus, 1880, p. 436; op. eit., p. 6, 1881; 

 Etoiles de Mer, p. 197, pi. iii, fig. 1, 1884; Exped. Trav. et Talisman, 

 p. 117, 1894. A, Agassiz, Three Cruises of the Blake, vol. ii, p. 105, 

 fig. 382. 



The largest specimen examined by me has the radii 10™™ and 

 lOSmm. pa^^i(j^ 1:10.5; diameter of rays at base 10™"°; height 

 11™™. 



The small disk is convex or a little swollen. The long slender 

 rays are well rounded at the base, but become somewhat carinate 

 on the attenuated distal half. 



The disk is occupied largely by the ten basal radial and inter- 

 radial plates, and a large prominent central plate, with a central 

 mamilla supporting a short obtuse spine. 



The dorsal radials are larger and more elevated than the inter- 

 radials and have a central boss, which bears a short obtuse spine. 

 They are rounded with small notches or emarginations around 

 the margin, where there are isolated papular pores. Similar 

 pores surround the central plate. 



The basal interradials are flatter and more angular and have 

 no central spine. They are in contact with the radials laterally. 

 One of them is partly covered by the madreporic plate, which is 

 rather large and convex, with radiating gyri. 



