ECHINONEUS CYCLOSTOMUS. 51 
that of a one-sided sphaeridium (fig. 3) from the odd anterior ambulacrum which 
contrasts with the circular chipped outline (fig. 4) and its ovoid mate, from the 
left anterior ambulacrum. Dissimilarity is also observable (fig. 6), where the 
first sphaeridium is ovoid and the other club-shaped; both came from the 
right anterior ambulacrum of a specimen 26 mm. long. 
It is noticeable that the five figures on Pl. 17, figs. 7-9, are not exactly like 
those on Pl. 16, figs. 1-4, although the specimens came from the same place, 
Fakarava Island. It should, however, be observed that they were taken from 
two specimens, one 12 mm. the other 23 mm. in length. 
ARRANGEMENT OF THE TUBERCLES AND SCROBICULAR CIRCLES. 
Plates 24, 25. 
De Loriol mentions the tubercles and scrobicular circles as specific charac- 
ters.' In perfect specimens, on the actinal side near the actinostome in the 
interambulacral area, the primary tubercles may be for the most part without 
a scrobicular area, but surrounded by large glassy tubercles. In other speci- 
mens of the same size, from the same locality, the boss is deeply set on the test, 
and the serobicular circles are transformed to open angular cells, with a small 
number of miliaries and a few minute glassy tubercles on their edges. (Pl. 25, 
fig. 9.) 
The primary tubercles on the actinal side are nearly uniform in size and 
arranged in horizontal rows. <A few of the plates nearest the actinostome have a 
single line, after this each plate has two; in the region of the ambitus, and for 
some distance above, the tubercles run diagonally as well as horizontally, and 
they vary in number according to age. They are smallest in the odd posterior 
interambulacrum. 
The seventh plate from the actinostome, including the primordial, in the 
left anterior interambulacrum of eight specimens from Port Antonio, measuring 
from 4.19 mm. to 17 mm. in length (with an interval of about two millimetres 
between each) is shown on PI. 25, figs. 7-8. In the smallest specimen, 4.19 mm. 
in length (fig. 1), this plate is on the abactinal side, and has, besides a few milia- 
ries, only two of the primary tubercles, one being towards the upper corner 
near the median line. In the next smallest, 6 mm. long, this seventh plate (fig. 2) 
is on the actinal side, and has its third tubercle near the upper outer corner; all 
1 Two specimens from Mauritius, 36 and 37 mm. in length, resemble de Loriol’s E. abnormalis, 
but the mamelon is without a perforation. 
