28 ASPIDODIADEMA JACOBYT. 
a narrow irregular vertical line, separating the arabulacral from the inter- 
ambulacral region. The primary spines of the two areas are similar, those 
of the ambulacra! areas being smaller and more slender. The secondaries, 
though not numerous, are remarkable for their uniform size in both areas, 
and their arrangement recalls to a certain extent that of the papillae of the 
Cidarida). In life the test is of a light gi-eenish pink color, the areolas 
darker; the secondary spines are of a light pinkish tint, darker at the base ; 
the primary radioles yellowish green, with a greenish chocolate base. In 
some specimens the test is also of this greenish chocolate color, the spines 
more whitish, or tending towards a dirty yellow. 
The sheathed pedicellarije are most numerous above the ambitus toward 
the abactinal region ; the shaft of the pedicellarifB is nearly as long as that 
of the secondary spines ; from their size the sheathed pedicellaria^ are very 
prominent objects on the test. 
The actinostome is covered by ten large buccal plates, as in A. hdcrotuhcr- 
culalum and A. untillarum, but these plates form a ring round the actinal open- 
ino-, leavins: a bare ring between them and the edge of the test. 
There are eight large elliptical plates round the anal opening, somewhat 
as in A. /onsimi, but having a larger ring covered by minute plates between 
them and the genital ring. The anal plates are closely tuberculated by 
miliaries nearly of the same size as the miliaries of the ocular plates ; the 
genital plates are coarsely and closely tuberculated by miliaries. 
Smaller specimens differ from the larger ones mainly in the lighter coloring 
of the test and spines, and the more flattened abactinal region of the test, 
which loses its peculiar Echinostrephus-like shape as it increases in size, 
becoming more regularly arched, as in Amblj'pneustes. The jDiates of the 
actinal and anal system cover a comparatively larger space in younger 
specimens. 
In a small specimen measuring about 3 mm., the anal plates appear as 
forming close to the genital ring ; the difference in size of the genital and 
ocular plates is already apparent. The anal proboscis is quite long at that 
stage, equalling in length the diameter of the anal system. 
In a specimen measuring 28 mm. in diameter, the anal system measured 
5.50 mm., the abactinal 10 mm., and the actinal 9 mm.; the height of the 
test was 20 mm.; and there were eleven and twelve plates in the inter- 
ambulacral areas. 
In a specimen measuring 12 mm. in diameter, the anal system measured 
