40 HAWAIIAN AND OTHEE PACIFIC ECHINI. 



distal sides being the smallest (PI. 39, fig. 2). The genital pores are near 

 the distal edge ; the specimen figured in PI. 39, fig. 2, is probably a male. 

 The genital plates are covered with well-separated secondary tubercles, all 

 more or less comma-shaped, especially in the area adjoining the anal system. 

 The madreporic genital is riddled with pores, and is covered with small 

 globular tubercles closely packed together (PL 39, fig. ?). The ocular 

 plates are heart-shaped, irregularly triangular, with rounded sides, and with 

 the exception of the right anterior one, come in contact with a large inter- 

 genital anal plate. The anal system is pointedly pentagonal, with an outer 

 ring of large, irregularly shaped" plates, an inner ring of irregularly shaped 

 smaller plates, and the smallest plates immediately round the anal opening. 

 The plates of the anal system carry a few tubercles similar to those of the 

 genital and ocular plates. 



The ambulacral plates of the actinal system are very narrow ; they are 

 edged with three small miliaries on each side of the central line of pores. 

 To the thirteen ambulacral plates in each vertical row only six interambu- 

 lacral plates correspond. 



In a smaller specimen measuring 24 mm. in diameter the ratio of the 

 diameter of the test to the length of the longest primary spine is somewhat 

 less than in the larger specimen. In this specimen the longest primary 

 spines are 65 mm. only, and the basal part of the radiole is fully one third 

 the lengtli of the whole spine. Although the test is proportionately much 

 flatter, only 12 mm. in height, there are already five and six interambulacral 

 plates. With diminishing size the flattening of the test also rapidly 

 increases. In a specimen 18 mm. in diameter, the height is 8 mm. (PI. 42, 

 figs, l-.'f), the longest primary spine is 48 mm., and there are five and six 

 primary tubercles. In a specimen 9 mm. in diameter, the height is 4 mm., 

 the longest spine is 14 mm. (PI. 42, figs. 7-10), and there are four and five 

 primary tubercles. In tlie smallest specimen examined, with three and four 

 primary tubercles, the diameter was 5 mm., and the height 2.25 mm. The 

 longest spines measure 12 and 14 mm. ; the basal part of the spine being 

 nearly one-half tlie length of the radiole. In small specimens the abactinal 

 system is smaller than the actinal. In the specimen figured in PI. 42, 

 figs. 1, 2, the abactinal system measures C.5 mm. and the actinal 7 mm. 

 across. In the specimen PI. 42, figs. 7, S, the abactinal system measures 

 3.5 mm., and the actinal 4 mm. In the smallest specimen, 5 mm. in 

 diameter, the abactinal and actinal system each measure 3 mm. 



