30 PANAMIC DEEP SEA ECHINI. 



The anal plates are, however, more characteristic of an older stage than 

 is usual in such a young specimen, the plates intercalated hetween the 

 primary anal plates equalling in size several of those of the primary ones. 

 In the oldest anal system figured (PI. 11, fig. 6) the second row of plates 

 have all become intercalated between the primary ones, as is already the 

 case in a younger specimen (PI. 11, fig. .7), the primary plates being only 

 slightly more prominent than the secondary ones. 



The primary radioles are cylindrical, finely striated (PI. 12, fig. /.'), they 

 early lose all trace of the delicate serration seen in the spines of the ambitus 

 and in younger specimens. In a small specimen 8 mm. in diameter there 

 are five primary tubercles, in one 23 mm. we find six, and in a specimen of 

 35 mm. there are eight. The radioles of a specimen 11 nun. are 31 mm. 

 long; of one 35 mm. they are 105 mm. 



In a specimen with eight primary tubercles the scrobicular area of the 

 larger tubercles joins the sutures of the plate below it, and is thus sur- 

 rounded by an imperfect circle of secondaries and miliaries (Pis. !). figs. 5, 6; 

 IK, fig. 9 ; 13, fig. .'). the rest of the plate being thickly covered with 

 secondaries and miliaries irregularly arranged. In a somewhat younger 

 specimen (PI. 10, fig. 7) there are as yet but few miliaries on the coronal 

 plates except on the older ones near the actinal system (PI. 10, figs. .', .;). 

 In still younger specimens the coronal plates are comparatively bare, and 

 carry only a single miliary at each angle of the interambulacral plates (PI. 

 10, figs. 4, 5). 



Part of the base of the secondary tubercles is frequently cut off by the 

 extension of the muscular attachment of the radiole beyond the scrobicular 

 area (PL 13, fig. 1). 



In the ambulacral areas each plate has at first but a single secondary 

 tubercle (PL 10, fig. .f); even in older specimens we find the same struc- 

 ture (PL 10, fig. 6) It is only in somewhat older specimens (PL 10, fig. 8) 

 that we occasionally find an additional miliary in the equatorial region of 

 the corona (PL 9, figs. 5, 6). The secondary ambulacral tubercles are 

 neither perforated nor crenulated. 



The actinal system is completely covered by the ambulacral buccal 

 plates, which spread laterally so as to unite, except near the last actinal 

 interambulacral plates, where a narrow space is left bare or is partly filled 

 by a single buccal interambulacral plate (PL 10, figs. 1, 2, ■>). 



In young specimens of 8 and 10 mm. in diameter the buccal plates, even 



