438 



,sti:o.\<;ylocextrotus. 



the actinal part of the poriferous zone is only slightly petaloid ; the arrange- 

 ment of the pores above and below the ambitus differing only slightly. All 

 the specimens examined are remarkably uniform in character; only very 

 few and slight variations have been observed in the specimens of different 

 collections, and this species seems to be one of the best characterized among 

 Echini. 



Mauritius ; Java ; Samoa. 



STRONGYLOCENTROTUS. 



Strongylocentrotus Brandt, 1835, Prod. Dcs. An. 

 (See Pari II. p. '.'76.) 



Strongylocentrotus albus 



Echinus albas Moi. in.. 17Si>. Chili. 



! Strongylocentrotus albus A. An . 1*72, Rev. Ech., ft. I. p. 162. 



Test high, thick, regularly arched, outline from above slightly pentagonal; 

 poriferous zone broader than the median ambulacra! region, which is Hanked 

 externally by two vertical rows of small primary tubercles; from their base 

 extend horizontal rows of secondary tubercles, from five to six in a row, 

 slightly slanting, increasing in size outwardly, which separate the arcs of 

 pores of the poriferous zone. The median ambulacral space is closely tilled 

 with secondary tubercles, the larger ones forming two irregular vertical rows 

 placed next to the outer large vertical row adjoining the poriferous zone. In 

 the interambulacral space there are two vertical rows of very prominent pri- 

 mary tubercles extending from the apex to the actiiiostome. situated half-way 

 between the poriferous zone and the median interambulacral line. The rest 

 of the coronal plate is closely packed with secondaries and miliaries arranged 

 in somewhat irregular horizontal rows; the secondary tubercles are slightly 

 larger towards the median line and near the poriferous zone. Near the ambi- 

 tus there are from ten to eleven pairs of pores in specimens with about thirty 

 to thirty-three coronal plates. The anal system is large, made up of closely 

 packed tuberculated plates, surrounded by a narrow ring of small genital 

 and ocular plates, the latter, all except one, excluded from the anal area. 



