REPORT ON THE ECHINOIDEA. 09 



immediately past the ambitus tlie primaries are reduced to a single vertical row of a 

 much smaller size than those of the actinal surface, placed in the central part of the 

 coronal plates and extending neai'ly of uniform size to the abactinal system. The rest of 

 the plate (PI. VII. fig. 5) carries a few secondaiy tubercles and miliaries irregularly 

 arranged, the former forming indistinct vertical rows, the latter indistinct horizontal lines. 

 The poriferous zone is of nearly uniform width, from the actinal edge to the apical 

 system. The actinal cuts (PL VII. fig. 3) encroach deeply upon the interambulacral 

 plates ; there is no tendency to expansion of the poriferous zone at the actinostomc 

 The bare median interambulacral spaces (PL VII. fig. 1) as seen from above are ill- 

 defined, and have not the prominence they take in Astropyga. The pedicellarise 

 of the lower surface are narrow-headed, elongate, with a long stem; they are similar 

 in the ambulacral and interambulacral areas of the actinal and abactinal sides. 

 The apical system (PL VII. fig. 6) is characterised by the small anal system covered 

 with numerous irregularly-shaped plates, carrying few miliaries near the genital edge. 

 The genital plates are uniform in size, pentagonal, with rounded points ; the genital 

 openings are large, and are placed near the pointed extremity as in the Diadematidse. 

 The macbeporic body is not prominent, the ocular plates are hexagonal, they carry five to 

 seven miliaries irregularly placed like those of the genital plates near the anal edge. 



In younger specimens (PL VII. figs. 7-9) the principal differences consist in the 

 comparatively larger size of the primary tubercles of the abactinal region, their smaller 

 number on the actinal surface and the larger size of the plates covering the anal system. 

 The genital plates are less elongated, the ocular and genital plates resembling at this early 

 stage in their arrangement that of the genital ring of Aspidodiadema. A young speci- 

 men measuring 26 mm. in diameter shows that in this species the changes due to growth 

 are readily traced ; they consist in the smaller number of coronal plates and the smaller 

 number of the primary and secondary tubercles, but their ultimate arrangement is 

 already indicated in this smaller specimen. The spines are, however, proportionally much 

 longer, equalling in length nearly one-haLf the diameter of the test. The spines in this 

 specimen are still white, only a few contain a slight trace of light violet pigment matter 

 tinting the extremity of the spines or forming irregular patches or transverse bands on the 

 spines. The imbricating plates of the actinal membrane are very distinct. The diff'erence 

 in size between the genital and ocular plates of the anal ring is hardly appreciable, it 

 was already quite small in that of the young specimen figured on Plate VII. fig. 9. 



In large specimens the colour of the test in alcohol is a dark violet, the spines of a 

 dark violet brown. 



Station 174. August 3, 1874. Lat. 19° 10' S., long. 178° 10' E. ; no fathoms on 

 label. Text. 255, 610, and 210 fathoms; bottom temperature at 600 fathoms, 37° C; 

 globigerina ooze. 



Station 219. March 10, 1875. Lat. 1° 50' S., long. 146° 42' E., 150 fathoms; mud. 



