392 PHYLLACANTHUS VERTICILLATA. 



these rings are narrow, close together, towards the extremity of the spine at 

 the base of the fluting. The general color of the papillae and secondary 

 spines is dark violet. 



Both in P. dubia and in P. imperialis there are but six large primary 

 tubercles in the largest specimens I have had occasion to examine (test 

 measuring 75"™ in diameter). The scrobicular circle of P. imperialis is well 

 defined, circular, limited by one row of rather prominent secondaries. The 

 mammary boss of primaries is prominent. 



In the abactinal system the madreporic genital plate is considerably larger 

 than the others ; genital openings small, removed from outer edge of genital 

 plates ; granulation of abactinal system close; ocular plates crescent-shaped, 

 with deep ocular pit equal in length to the width of the genital plates. 

 Plates of anal system are small, with the exception of a row of large exterior 

 ones opposite the madreporic genital plate, and gradually diminish towards 

 the madreporic plate. 



Median interambulacral space broad, covered by numerous irregular mili- 

 aries ; the median ambulacra! zone only slightly broader than the poriferous 

 zone, with four to five irregular vertical rows of miliaries closely crowded 

 together between the exterior rows. 



Rod Sea; East India Islands; Australia. 



Fhyllacanthus verticillata 



! Cidarite* verticillata Lamk., 1816, An. s. Vert. 



'Phyllacanthus verticillata A. Ag., 1872, Rev. Ech., Ft. I. 



PL P. f. 40-42"; Pl.P.f.7. 

 This species, which is so well known from its peculiar spines, swollen at 

 intervals along the shaft, has a test equally characteristic. The median 

 interambulacral space is smooth, totally bare ; the secondary tubercles are 

 limited, in each coronal plate, to the single row forming the scrobicular 

 circle, with but few irregularly scattered tubercles on each side of it, 

 towards the outer edge of the plate. The primary tubercles are small, not 

 prominent. The median ambulacral space, which is much broader than 

 the poriferous zone, is also nearly smooth, with the exception of an extremely 

 irresrular vertical row of miliaries flanking the two vertical rows of miliaries, 

 adjoining the outer secondary rows. This median space is slightly sunken, 

 the outer rows of secondaries adjoining the poriferous zone becoming thus 

 exceedingly prominent. The color of the secondary spines and papilla? is 



