STRONGYLOCENTROTUS ARMIGER. 439 



Surrounding the anal system the genital plates carry quite large secondary 

 tubercles. Genital openings large ; madreporic genital slightly larger than 

 the other genital plates. Actinal membrane smooth, excepting a few clusters 

 of well-separated plates in continuation of the ambulacra. 



Color of test brownish ; spines short, moderately stout, greenish, tipped 

 with white. 



Patagonia ; Chili ; Peru. 



Strongylocentrotus armiger 



! Strongylocentrotus armiger A. Ac, 1872, Bull. M. C. Z., III. 



PL V.f. 1. 



Test thin, flattened above, regularly arched below. Is at once distin- 

 guished from its congeners by the peculiar short thick swollen spines, 

 resembling those of Echinometra oblonga. The test, when denuded, shows 

 that the largest primary tubercles of both areas are not placed near the 

 ambitus, but, on the contrary, within three plates of the abactinal system in 

 the interambulacral space ; they cover the abactinal part of the flattened test, 

 decreasing rapidly towards the ambitus and actinal surface. 



The genital plates are small ; the genital openings large, exterior ; anal 

 system large ; the plates covered by small secondary spines and tubercles. 

 Madreporic genital much larger than the other genital plates. The two 

 principal vertical rows of tubercles of the ambulacral region are closely 

 packed, with secondaiy tubercles in the narrow median space forming only 

 a short very indistinct row for a part of the space. Poriferous zone broad ; 

 pores arranged in well-shaped arcs. The principal row of primary inter- 

 ambulacral tubercles is flanked exteriorly by smaller secondaries, separating 

 them from the poriferous zones by an irregular vertical row. There are two 

 median vertical rows of still smaller secondaries. The coronal plates are 

 narrow, the larger tubercles occupy nearly the whole plate ; the rest of the 

 plate is filled by small secondaries arranged round the base, with but few 

 miliaries, both in the ambulacral and interambulacral spaces. In the ambu- 

 lacral zone a few small secondaries extend between the arcs of the poriferous 

 zone. 



