56 HAWAIIAN AND OTHER PACIFIC ECHINI. 



specimen of Pattersoni 11.5 mm. in diameter is more globular, being 9 mm. 

 in height. The proportions of the actinal and abactinal systems are nearly 

 the same ; in *S'. cinda the abactinal system is 7 mm. in greatest diameter, 

 the actinal, 5.7 mm; in S. Pattersoni they are 7.5 mm. and 5.6 mm. 

 The interambulacral system is composed of six or seven primary plates in 

 each column. The primary tubercles are comparatively small, the median 

 edge of the plates being occupied by rather large secondary tubercles (PI. 

 52, fig. 11) set closely together and forming two vertical lines, with a deeply 

 sunken and narrow groove between tliem, giving the interambulacral face of 

 the test much the appearance of having a sunken groove as in Goniocidaris 

 canaliculata. This feature is scarcely shown in PI. 52, figs. 8 and 11, as the 

 drawing is not shaded. On the edge of the plate adjoining the ambulacral 

 system there are only two secondary tubercles, one in each angle of the 

 coronal plate (PI. 52, fig. 11). 



In the ambulacral system there are either 14 or 15 plates of nearly uni- 

 form size in each column. Each plate carries a primary tubercle and, except 

 the uppermost and lowermost, one or two secondaries. These plates are 

 made up of two components which are abactinally of nearly equal size but 

 actinally appear more clearly as a primary plate and an accessory plate. 

 The Hemicidaris character of the actinal ambulacral tubercles is but 

 slightly developed (PI. 52, figs. 8, 10). 



The actinal system is covered by six more or less concentric series of 

 irregularly pentagonal or hexagonal plates, the pairs of poriferous plates 

 forming the most prominent series ; these pairs are separated from each 

 other by a set of narrow intercalated plates connecting the actinal with the 

 outer rows. 



The abactinal system is very striking from the prominent horseshoe- 

 shaped ridge which borders the ocular plates (PL 52, fig. 9) and the regular 

 lieptagonal outline of the lateral genital plates. The suranal plate, the odd 

 genital, the right posterior ocular and the right posterior genital plates 

 surround the anal system. This is covered with small irrcLTularlv ar- 

 ranged pentagonal or polygonal plates, the larger plates carrying a single 

 minute miliary. The ocular plates are of uniform size, with the exception 

 of the right posterior ocular, which is somewhat smaller. The genital ring 

 and the suranal plate are covered with a fine granulation; a small heart- 

 shaped shield covers the surface of the oculars, which appear like triangular 

 plates with convex pointed sides cutting into the genital ring, but owing 



