THE GENUS COLOBOCENTROTUS. 19 



Figs. 9-11 are drawings of the characteristic stout elliptical radioles of 

 P. atrata, rounded or slightly pointed at the extremity, taken from the 

 ambitus where they form a ring at the base of the pavement of polygonal 

 radioles extending from the abactinal side of the ambitus to the apex. The 

 ambital radioles are from 15 to 20 mm. in length, and of a dark violet color, 

 almost black on the upper side ; on the actinal side the color of the spines 

 is yellowish or light brown. These large radioles are finely striated, of a 

 dark violet, with a well-marked milled ring. Blamville writes " d'un violet 

 fonq^ presque noir." 



Figs. 12-U are views of short triangular radioles from the ambitus which 

 form a part of the abactinal polygonal pavement of the test ; they are taken 

 from the left posterior interambulacrum. 



Figs. 15-17, views of a somewhat mushroom-shaped hexagonal or polygonal 

 radiole taken from the abactinal side of the ambitus, from the right posterior 

 ambulacrum. 



Figs. 18-20 and figs. 21-23 are polygonal radioles taken from the right 

 anterior interambulacrum from the abactinal side of the ambitus ; and figs. 

 24, 25 is a similar radiole taken from the right posterior interambulacrum. 



Figs. 26-28, drawings of a low mushroom-shaped asymmetrical polygonal 

 radiole taken from half way between the ambitus and the abactinal system. 



Figs. 29-31 is an irregularly hexagonal radiole taken from the genital 

 plates ; fig. 32 is a radiole taken from the madreporic genital ; and fig. S3 

 represents a miliary spine hidden by the large pavement of abactinal primary 

 radioles. 



It will be seen on examining the figures of radioles given on Plate 23 that, 

 with the exception of the spines of the actinal side and of the miliary spines, 

 all the radioles are asymmetrical. 



The striking difference between the radioles of Podophora pedifera and 

 those of Podophora atrata is well shown on comparing PI. 11, figs. 11-13; 

 U-16; 17, 18; 20-21; 22-21t; 25-27; 28-30; 31-33 with. Plate 23, figs./-5; 9- ^i 

 11; 12-lk; 15-17 ; 18-20; 21-23; 26-28; 29-31. The most marked differences / 

 are in those of the ambital radioles (compare PI. 11, figs. 11-13 with PI. 23, 

 figs. 9-11). 



Podophora pedifera Agass. 

 Plates 1; 3% figs. 1-4; 4-16, figs. 1-8; 31, figs. 1-i. 



This species was figured in the Revision of the Echini (PI. IIF, fig. S), 

 under the name of Colobocentrotus atratus, and noted as having been collected 



