14 SALEXIA PATTEIiSOXl. 
like spines found near tlie actinostome. The papillae or secondary spines are 
long, with a rounded slightly concave extremity. The outer edge of the abac- 
tinal system and the median line of the ambulacral area are thickly studded 
with minute globular jiedicellari*. The plates of the abactinal system are 
covered by a coarse granulation ; this towards the outer edge of the geni- 
tal plates becomes minute sessile spines. The sutures between the genital 
plates, as well as the lines separating them from the abactinal part of the 
ocular plates, are deep. The anal system carries short, stout, pointed spines. 
None of the genital pores, with the excej)tion of the madreporic genital, are 
very distinct ; the madreporite consists of a few minute pores adjoining the 
large genital pore. The ocular plate opposite the superanal plate nearly 
touches the anal system, approaching it much closer than is the case in 
S. varispina. 
In specimens measuring 12 mm. in diameter, there are usually from five to 
seven primary tubercles in tlie interambulacral area. The secondai'y tuber- 
cles, carrying the flat papilhe, are arranged vertically in open arcs round 
them; and these arcs, running together along the median interambulacral 
line, form two wavy vertical rows of tubercles, closely packed, which gives 
to the median interambulacral area a somewhat sunken aspect, as in Go- 
niocidaris. The ambulacral tubercles, as in *S'. rtii-ispiita, resemble in their 
arrangement those of Ilemicidaris, forming two vertical rows ; they are 
largest near the ambitus, diminish rapidly iu size towards the actinostome, 
and more gradually towards the apical system. The largest ambulacral 
tubercles are not larger than the secondaries surrounding the primaries of 
the interambulacral area. The ambulacral zone is narrow ; the pores are 
arranged in a slightly undulating line, following irregularly the outline of the 
pi'imary plates in the interambulacral area. Smaller and larger specimens 
differ only in the size of the primary tubercles, those towards the actinos- 
tome increasing but slowly in size as the diameter of the test enlarges. The 
principal differences to be noticed are in the greater number of imbricating 
plates which cover the actinal membrane in the older specimens, as compared 
with the more simjile arrangement of the plates and their smaller number in 
earlier stages. In 3'ounger specimens the five pairs of large buccal tentacles 
cover nearly the whole actinostome ; they next become separated from the 
actinal edge of the test by a few irregularly arranged imbricating plates, and 
as the rows of plates increase they form also narrow zones between the pairs 
of buccal plates in extension of the interambulacral areas, until in the older 
