PHYLLACANTHUS IMPERIALIST 391 



papillae ; hence the bare appearance of this region even when the test is not 

 denuded. The secondaries forming the scrobicular circle are not large, and 

 at the horizontal junction of two scrobicular circles become much smaller, 

 and the scrobicular circle more or less indistinct. 



The median ambulacra! zone is crowded with miliaries similar to those 

 of the interambulacral zone, forming from eight to ten irregular vertical 

 rows ; the outer rows adjoining the poriferous zones consist of small secondary 

 tubercles, carrying extremely elongate secondary spines of a grayish-green 

 color, slightly darker at top of spine. The poriferous zone itself is pro- 

 portionally narrower than in other species of the genus, compared to the 

 great width of the ambulacral system. 



Genital plates in contact laterally, of nearly uniform size ; genital openings 

 near centre of plates. Anal system small, covered by close granulation, 

 formed of miliaries like those of the median ambulacral and interambulacral 

 zones, and carrying similar papilla?. Ocular plates cordiform, separated from 

 the genital plates by well-marked sutures between adjoining plates. The 

 primary spines are more or less cylindrical, slightly tapering, with large 

 spines along the whole length of the shaft, arranged in from six to eight 

 irregular longitudinal rows, or with lamella? forming ridges at the extremity 

 of the spines, and extending towards base of spine, or with the shafts of 

 the spines ornamented by irregular longitudinal rows of from six to eight 

 small disconnected lamella? ; the color in alcohol is greenish, with dark 

 olive-colored spines. 



Sandwich Islands. 

 FhyUacanthus imperialis 



! Ciduriles imperialis Lam., 1816, An. s. Vert. 

 Phyllacanthus imperialis Br., 1835, Prod. Des. An. 



PI P. f. l-e; PlP.f.e. 



The primary spines of this species have a general resemblance to those of 

 Heterocentrotus mammillatus. Though apparently smooth, they are covered 

 by a uniformly packed close granulation, arranged in more or less close irregu- 

 lar longitudinal lines. Extremity of spines fluted ; bare base of spine above 

 milled ring not rigidly defined, striation of base passing gradually into 

 granulation of the shaft. The spines are frequently ringed with two or 

 three broad bands of yellow upon the dark violet ground of the shaft of the 

 spine, which fades towards the base of the spines. In young specimens 



