60 THE VOYAGE OF H.M.S. CHALLENGEE. 



extend down towards the ambitus so far that the extremity of the poriferous zone is placed 

 at a point nearly half-way between the anal opening and the ambitus, far below its position 

 in Podociclaris sculpta. In both of these specimens the anal system was covered by five 

 plates (PL XXXIV. fig. 15) developed equally. The miliaries of the genital plates are larger 

 and more prominent than those of the coronal plates. The madreporic body is but little 

 developed, consisting merely of three to five indistinct pores. In the larger specimen the 

 genital openings are small l^ut sharply defined, and placed excentrically nearer the anal 

 edge, as they are in Podocidaris sculpta. 



The proportions of the abactinal system are somewhat diff"erent in the two species. 

 In Podocidaris prionigera, the diameter of the test being 9 mm., the abactinal system is 

 6 mm., whUein Podocidaris scidpta it occupies a comparatively smaU part of the abactinal 

 region (see Revision of the Echini, pi. iv. figs. 6, 8). The actinal system also is compara- 

 tively larger in the proportion of 5 to 9 to the diameter of the test ; while it is only 

 as 2 to 5 in Podocidaris scidpta. On the actinal side the ambulacral suckers are large 

 and powerful ; they diminish in size towards the ambitus, and become more distant and 

 pointed as they approach the abactinal system. 



Station 218. March 1, 1875. Lat. 2° 33' S., long. 144° 4' E. ; 1070 fathoms; 

 bottom temperature, 2"1° C. ; globigerina ooze. 



Station 205. November 13, 1874. Lat. 16° 42'N., long, 119° 22' E.; 1050 fathoms; 

 bottom temperature, 2'4° C. ; grey ooze. 



Podocidaris scidpta. 



Podocidaris sculpta, A. Agassiz, 1869, Bull. Mus. Comp. Zool., vol. i. 

 Station 24. March 25, 1873. Ofi" Culebra Island ; 390 fathoms ; mud. 



Ccelopleurus. 



Ccelopleurus, Agassiz, 1840, Cat. Syst. Ectyj}. 



Cailopletinis maillardi (Pis. V., VI., XXXVIII. figs. 7-9 ; PI. XLV. figs. 1-6). 



Keraiaphorus Maillardi, Mich., 1862, Maill. Bourbon. Ann. A. 



Ccelopleurus Maillardi, A. Agassiz, 1871, BuU. Mus. Comp. Zool., vol. ii. p. 456. 



This remarkable Sea-urchin was first described by Michelin under the name of 

 Keraiaphorus. He did not, however, suspect its close affinities to the Arbaciadse, and 

 Llitken was the first to hint at its identity with Coilopleurus, which a comparison I 

 subsequently made of small specimens dredged by the " Hassler" with Michelin's figures 

 fuUy corroborates. 



