20 TEOPICAL 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 Podojyhora pedifera is character- 

 istic of the Eastern Pacific, extending from Peru and Chili as far as the 

 Western Paumotus, while the typical Podojihora 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 (Pis. 7, figs. 1-3 ; 9, figs. J^-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 (PI. 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 Pis. 20, tigs. 3, 5 ; 21, figs. J^~6 with Pis. 7, 

 figs. 2,3; 9, figs. 5, 6). The outline of the test is higher, more arched in 

 P. pedifera (Pis. 7, fig. 3; 8, fig. 3; 9, figs. 3, 6) than in P. atrata, which is 

 flatter and slightly conical (Pis. 20, figs. 5, 6; 21, figs. 3, 6). P. atrata is very 

 much flatter on the actinal side (Pis. 20, figs. 1, 2, 6; 21, figs. 1, 3, 4) than 

 P. pedifera in which the actinostome is somewhat sunken (Pis. 8, figs. 1, 3; 9, 

 figs. 1, 3, Jt). The ambulacral poriferous zone is also proportionally much wider 

 in P. pedifera (Pis. 8, fig. 1; 9, fig. l) than in P. atrata (Pis. 20, fig. 2; 21, 

 fig. 1) where the median rows of tubercles of the ambulacral zone extend far 

 towards the actinostome (Pis. 20, fig. 2; 21, fig. i), while in P. pedifera the 

 corresponding ambulacral tubercles extend but little beyond the ambitus 

 (Pis. 8, fig. 1; 9, fig. i). The actinal interambulacral zone is also much broader 



