128 HAWAIIAN AND OTHEK PACIFIC ECHINI. 



or less perfect pentagon round the actinostome, about one third of the 

 distance to the ambitus. 



The primary radioles are slender (PI. 56, figs. 6, 7; 59, figs. 1, 2), of 

 moderate but variable length, the longest equalling the diameter of the test. 

 They are decidedly flattened, nearly white, but many have a purplish longi- 

 tudinal stripe on the abactinal side, and not infrequently they are hand- 

 somely banded with purple (PI. 56, fig. 6). The whole length of the shaft 

 is finely serrated in close longitudinal lines. The verticillation is very deli- 

 cate, caused by longitudinal furrows alternating with the irregular longi- 

 tudinal rows of minute teeth (PI. 56, figs. 6, 7). 



The aspect of this species as seen from the abactinal surface (PI. 59, 

 fig. ^), with its primary spines limited to the ambitus and extending but a 

 few plates towards the abactinal system, and its bare abactinal interambula- 

 cral areas with the few scattered, thin, sharp secondary spines, is in striking 

 contrast to its appearance as seen from the actinal side (PI. 59, fig. 1) ; see 

 also Mortensen, Siam. Echini, PI. 1, fig. 21. The primary spines are limited 

 to the vicinity of the ambitus, and on the rest of the actinal surface the 

 secondary and miliary spines are short, slightly curved or club-shaped, and 

 flattened at the tip and striated; so that on a first examination it would seem as 

 if the actinostome with its small spines extended far out towards the ambitus. 



The specimens range in diameter from 42 to 70 mm. The test is very 

 flat, the greatest height being only .25-30 of the diameter (PI. 59, fig. 5), 

 the abactinal system is .30-.42, and the actinal only .17-.24 of the diameter, 

 while the anal system is .60-. 65 of the abactinal. The test is relatively 

 higher, and the abactinal and actinal systems larger, in small than in large 

 individuals. 



Dr. Mortensen, after laying great stress (by printing it in capitals) 

 upon the uniform granulation of the actinal surface as typical of the 

 genus Chaetodiadema, modifies this in ordinary print a few pages further 

 on, when describing Ch. japonicwn. 



One of the most striking characters of this interesting species is the 

 extraordinary scarcity of pedicellaria3. Careful and long-continued ex- 

 aujination of ten specimens brought to light only a single tridentate pedi- 

 cellaria, and that had the tip broken off. It was of the slender irideuiaU 

 form, with the valves meeting only near the tip. These valves (PI. 50. figs. 

 IG, 77) when complete would have measured about a millimeter and a half in 

 length, with the strongly compressed blade hardly a tenth as wide. The 



