40 THE VOYAGE OF H.M.S. CHALLENGER. 



fig. 4) sliows two such spines (the bLack ones on the left) simihir to those covering the 

 whole test of this specimen. 



Samboangan ; 10 fathoms. 



Station 201. October 26, 1874. Lat. 7' 3' N., long. 121' 48' E. ; 82 fathoms and 

 102 fathoms; stones and gravel. 



Phyllacanthus gigantea. 



Cliondroeidaris girjantea, A. Agassiz, 1863, Bull. Mus. Comp. Zool., vol. i. 

 Phijllacantlius gigantea, A. Agassiz, 1872, Eevis. Eoh., part 1, ]}. 150. 



Ofi" Honolulu Reef. 

 Phyllacanthus verticillata. 



Cidarites verticillata, Lamk., 1816, Anim. sans Vert. 

 Phyllacantlius verticillata, A. Agassiz, 1872, Eevis. Ech., part 1. 



Station 186. September 8, 1874. Lat. 10° 30' S., long. 142° 18' E. ; 8 fathoms; 

 coral sand. 



Porocidaris. 

 Porocidaris, Des., 1854, Syn. Ech. Foss., p. 46. 

 *Porocidaris elegans (PI. Ill, XXXVIII. figs. 12-16 ; PI. XLIV. figs. 6-14). 



Porocidaris elegans, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 198. 



This species can at once be distinguished from Porocidaris 2>urpurata, Wy. T., by the 

 facies of the spines (PI. III. fig. 1) and by the structure of the abactinal system (PI. III. 

 fig. 2). The interambulacral plates of the test also differ from those of Porocidaris 2^ur- 

 purata in having a larger row of secondary tubercles surrounding the scrobicular circle 

 (PL III. fig. 5). This is complete only in the first and second of the coronal plates 

 nearest the abactinal system, the areas becoming confiuent towards the ambitus and 

 actinostome in the remaining plates. The median interambulacral space also difi"ers 

 from that of Porocidaris purpurata in having larger secondary tubercles, leaving a space 

 nearly bare between the secondaries, or only sparsely covered by small irregularly 

 arranged miliaries. There is a single row of small secondaries regularly arranged in a 

 vertical line along the median ambulacral space (PI. III. fig. 6.) with a few intervening 

 miliaries along the median line. The pores are distinct, separated by a prominent 

 median ridge. The primary interambulacral tubercles are surrounded by a large areola. 

 They are small, crenulate, except the last foi-med near the actinal system. 



