DS TROPICAL PACIFIC ECHINI. 
are from West Indian specimens, figs. 72 and 74 from specimens taken in the 
Pacific. 
At the smaller inner end, the plate (PI. 28, figs. 5, 6, 12) is prolonged slightly 
beyond the adjoining surface in some of the Makemo and Jamaican specimens. 
This is quite different from what is seen in a Barbados specimen, where the pro- 
jection can easily be recognized, though placed in a reéntrant curve (Pl. 28, 
figs. 8, 9). In another specimen from Fakarava Island the inner end of the 
plate (PI. 28, fig. 14) is almost straight. 
Close to the base of the disk on the lower side there is a set of two or more 
layers of yoke-shaped spicules (Pl. 28, figs. 2, 3, 7); these are nearly straight with 
a few small perforations on the inner side of the spicule. The tube-feet on the 
actinal, and on the greater part of abactinal side, seem to be without any other 
spicules, but in some of the tube-feet near the ocular plates a number of slender 
rods (fig. 10) were found; the disk plates were only rudimentary. 
The changes in the appearance of the disk may be due as much to their 
position on the test as to growth, as may be seen in three Jamaican specimens. 
In a specimen 25 mm. long the tube-feet of the actinal side, near the mouth 
(fig. 5) with disks 0.22 mm. across, are very different from those near the apical 
system (fig. 6) with disks only 0.14 mm. wide. But-in much younger specimens, 
the first formed tube-feet (fig. 4) which are found close to the mouth, are similar 
to the newly formed ones near the ocular plate. Apparently the difference 
between figs. 17, 12, from the actinal side of the test, and fig. 73, from near the 
ocular plate, in the specimen from Makemo, is due to difference in age. 
THe PERIPODIA. 
Plate 28, figs. 15-24. 
A comparison of the peripodia in a number of specimens, both young and 
adult, from various localities, does not reveal any reliable specific character, 
as the shape of the peripodium changes in form, size, and position on the different 
plates. 
Of four peripodia (Pl. 28, figs. 15-18), from a specimen 34 mm. long, from 
Lord Howe Island, the first one at the edge of the actinostome (fig. 15), is singly 
perforated, and placed vertically on the plate. The fifth from the actinostome, 
(fig. 16), with its great horizontal perforations, is the largest; the smallest is 
attached to the ambitus, and is placed diagonally on the outer part of the plate. 
These and one of the youngest peripodia near the ocular plate, with its oval 
