14 TROPICAL PACIFIC ECHINI. 
above the ambitus; they are highly asymmetric, fan-shaped, and polygonal 
(Pl. 40, figs. 12-14) ; somewhat more abactinally from the ambitus the polyg- 
onal radioles are smaller (Pl. 40, figs. 15-17) ; midway between the ambitus and 
the abactinal system the primary radioles of the odd ambulacrum are slightly 
smaller than those nearer the ambitus (compare Pl. 40, figs. 18-20, to Pl. 40, 
figs. 21-23); nearer the abactinal system the radioles have become still 
smaller (Pl. 40, figs. 24, 25; and Pl. 40, figs. 26, 27). Pl. 40, fig. 28, is 
one of the miliary spines from the upper extremity of the right posterior 
interambulacrum, hidden by the larger primary radioles. Figures of 
some of the primary radioles of the anal system are given on Ph 40, figs, 
29-32. 
Seen from the interior, there is a small triangular plate between the actinal 
plates of the odd posterior interambulacrum (PI. 43, fig. 7) and of the right 
anterior interambulacrum, which may be the remnant of the primordial plates 
of these interambulacra. 
Popornora Agass. 
Podophora atrata Agass. 
Pls. 2, figs. 1-3; 5%, figs. 5-8; 16, figs. 9-14; 17-28; 31, figs. 5-8. 
A fine specimen of Podophora atrata, measuring 97 mm. including the 
spines, is figured on Pl. 21%. It was collected, with others, by the Hon. 
Nicolas Pike, at Mauritius. When seen from above, it is of a dark violet, 
almost black; seen from the actinal side the marginal spines are of a light 
violet color towards the tip, passing to a very light shade of the same color. 
The smaller flattened and elongated actinal spines, as well as the miliary spines 
of the buccal plates, are of the latter shade; the actinal membrane is chocolate 
brown. The larger marginal spines are of a somewhat lighter color on the 
upper side, with a tinge of green; the upper surface is also coarsely and 
irregularly granular and pitted. On the lower side they are smooth or only 
slightly pitted near the tip. 
A very interesting specimen of Podophora atrata from Mauritius is figured 
on Plate 21%, figs. 1-3. It is marked for the abnormal development of a number 
of the ambital radioles. Instead of being merely cylindrical as is the case in 
the large majority of the specimens examined they are club-shaped and pro- 
portionally larger than the ambital radioles usually are. Their shape reminds 
one somewhat of the club-shaped spines of Cidaris Blumenbachit. 
