20 TROPICAL PACIFIC ECHINI. 
at Callao. A number of specimens were collected by the “ Albatross” at 
Fakarava on the sea-face of the reef, during the Tropical Pacific Expedition, 
1899-1900. An alcoholic specimen in the Museum collection is labelled 
Valparaiso? It would seem, therefore, that Podophora pedifera is character- 
istic of the Eastern Pacific, extending from Peru and Chili as far as the 
Western Paumotus, while the typical Podophora atrata, figured by Blainville, 
extends from the Hawaiian Islands to Mauritius, the Seychelles, and Zanzibar. 
Seen from above the color of the test is olive green, darkest near the 
abactinal system, the pavement of radioles near the ambitus becoming lighter 
in color with a purplish tint; the large marginal spines are greenish with an 
occasional tinge of purple. Seen from the actinal side the color of the margi- 
nal and flattened elongated actinal spines is of a dirty yellow color, the large 
marginal radioles being of a light brownish pink at the tip. The actinal 
membrane is dark brown. 
Podophora pedifera and Podophora atrata are readily distinguished. The 
row of primary, flat, truncated radioles which forms a close ring round the 
test at the ambitus in P. pedifera (Pls. 7, figs. 1-3 ; 9, figs. 4-6) is in striking 
contrast to the corresponding ring of radioles in P. atrata, which consists 
of flattened elliptical radioles rounded at the tip and well separated one from 
the other (Pl. 20, figs. 1, 3, 5). A comparison of the corresponding figures 
of Plates 7, 9, and Plates 20, 21°, 21°, shows this contrast at once. The 
abactinal radioles of P. pedifera above the ambitus form a close pavement of 
irregularly shaped low radioles closely fitting together, of a prevailing hexagonal 
outline, while the corresponding pavement of the low radioles of P. atrata 
consists of radioles of a rather rhomboidal or pentagonal outline and less 
frequently hexagonal (compare Pls. 20, figs. 3,5; 21, figs. 4-6 with Pls. 7, 
figs. 2, 3; 9, figs. 5, 6). The outline of the test is higher, more arched in 
P. pedifera (Pls. 7, fig. 3; 8, fig. 3; 9, figs. 3, 6) than in P. atrata, which is 
flatter and slightly conical (Pls. 20, figs. 5, 6; 21, figs. 3,6). P. atrata is very 
much flatter on the actinal side (Pls. 20, figs. 1, 2, 6; 21, figs. 1, 3, 4) than 
P. pedifera in which the actinostome is somewhat sunken (Pls. 8, figs. 1, 3; 9, 
figs. 1,3,4). The ambulacral poriferous zone is also proportionally much wider 
in P. pedifera (Pls. 8, fig. 1; 9, fig. 1) than in P. atrata (Pls. 20, fig. 2; 21, 
fig. 1) where the median rows of tubercles of the ambulacral zone extend far 
towards the actinostome (Pls. 20, fig. 2; 21, fig. 2), while in P. pedifera the 
corresponding ambulacral tubercles extend but little beyond the ambitus 
(Pls. 8, fig. 2; 9, fig. 2). The actinal interambulacral zone is also much broader 
