298 HAWAIIAN AND OTHER PACIFIC ECHINI. 



3.5. There are about eight coronal plates in each column in both ambulacral 

 and interambulacral areas. The primary spines are all broken but in a smaller 

 specimen, 5 mm. in diameter, they are 4-5 mm. long, and thus equal to h. d. 

 The sculpturing of the test is well marked in the mid-zone and actinally but 

 abactinally the plates become quite smooth, particularly the plates of the 

 abactinal system itself. The latter are also remarkable for their relatively large 

 size and freedom from tubercles. The genital plates (PI. 100, fig. 3) are nearly 

 of a size, though 1 is somewhat smaller than the others. Each plate carries a 

 minute tubercle on the distal margin, and the madreporic genital may have 

 one or two smaller ones in addition. The genital pore is conspicuous and is 

 surrounded by a raised ring. The madreporic pores are very few, only 6-10 in 

 number; they are situated in an elevation of the plate surface. The ocular 

 plates are nearly triangular and carry several minute tubercles, one of which 

 may be distinctly larger than the others. In the largest specimen, the oculars 

 are all excluded from the periproct, but in the others ocular I is more or less 

 broadly insert. The periproct is very large and is covered by a huge suranal, 

 nearly as big as a genital, and a number of very small plates near the anus, 

 which lies very close to genital 1 . None of the periproctal plates carry tubercles 

 of any kind. The ambulacra are decidedly narrower than the interambulacra 

 at the ambitus. The poriferous areas are very narrow and the arcs of pores 

 are vertical or nearly so. The primary tubercles are of quite unequal sizes, 

 particularly in the ambulacra. 



The actinostome (PL 100, fig. 2) is decidedly smaller than the abactinal 

 system. The membrane is thin and perfectly naked save for the minute buccal 

 plates. The latter are very remarkable for their relative size and arrangement. 

 At first sight there seem to be but five, as shown in fig. 2, PL 100, but more 

 careful examination shows that instead of a single plate in each ambulacrum 

 there are really two lying closely side by side, one of normal size with a well- 

 developed tube-foot and the other very small and with no trace of a tube-foot. 

 Placing the specimen with the mouth up and ambulacrum III anterior, it is seen 

 that, beginning in ambulacrum I, the small and large plates are arranged in the 

 following sequence small, large; small, large; large, small; small, large; 

 large, small; that is the large plates are 16, 116, Ilia, IV6, Va. It will be noted 

 that while this is the reverse of Loven's formula, it accords exactly with what 

 Loven shows to be the condition in a very young Strongylocentrotus ("Echino- 

 logica," PL IV, fig. 25) and what Jackson found in young Echinus (Mem. Boston 

 Soc. Nat. Hist., VII, p. 119), for in these cases only one plate of each pair of 



