POROCIDARIS VARIABILIS. 33 



white, in marked contrast to the dark-brown color of the base of the 

 radiole above the milled ring and with the brown of tne heavily fluted tip 

 of the radiole. The large radioles are frequently infested with numerous 

 specimens of a small species of Scalpellum (Pis. 16-21). The secondary 

 spines (Pi. 8, figs. 21-2^) are slender, pointed, flattened or rounded or 

 slightly dished, and finely fluted. 



Seen from above (Pis. 17, 21) the test is a dark violet or chocolate- 

 brown ; the abactinal system is the darkest and towards the equatorial 

 region of the test the color of the ambulacral and interambulacral spines 

 becomes somewhat lighter, of a greenish tinge at the tip. From these stand 

 out prominently the yellowish or brownish or whitish primary spines. 



The specimens figured on PI. 23, figs. 1-jf. and on PI. 22 are of a much 

 lighter color. In the specimen of PI. 22 the ambulacral and interambulacral 

 spines are of a light yellowish-brown color, and those of the specimen fig- 

 ured on PL 23, figs. 1-4 are of a still lighter color. On the whole, judging 

 from the specimens at our disposal, the color increases in depth with size. 



In a specimen 72 mm. in diameter (Pis. 18, 19) and 50 mm. in height, 

 there are eight and nine interambulacral plates. The primary tubercles are 

 perforate, but irregularly crenulated (PI. 19). The scrobicular area is sur- 

 rounded with secondaries only slightly larger than those of the median 

 interambulacral space and filling the angles of the interambulacral plates 

 next to the poriferous zone (PI. 19, fig. 2). The scrobicular areas below 

 the equatorial zone are slightly confluent. The median ambulacral zone is 

 slightly broader than the poriferous zone. It is undulating, separated from 

 the poriferous zone by an outer vertical row of secondaries, the median 

 belt carrying miliaries forming irregular vertical rows. The inner row of 

 pores is somewhat larger than the outer row (PI. 19, fig. 1). The abactinal 

 system (PI. 18, fig. ;?) is circular, 31 mm. in diameter. The madreporic 

 genital is far larger than the others ; they all are irregularly heptagonal ; 

 the ocular plates are small, heart-shaped, and are all excluded from the 

 anal system. The anal system is sharply pentagonal, with a large outer 

 row of anal plates; there is a second row of smaller plates adjoining the 

 irregularly arranged minute plates which surround the anal opening. The 

 miliaries on the genital plates are limited in their distribution ; they are 

 small, comparatively few in number, and irregularly arranged round the 

 genital pores. On the oculars they occur on the median belt of the plate. 

 The larger anal plates carry from one to three secondaries, with a few 



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