THE GENUS COLOBOCENTROTUS. 25 



The ambulacral radicles near the ambitus (PL 11, figs. 9, 10), are the first 

 to show a marked flattening and to approach in outline the large, 

 flattened, spatula-shaped radioles of the ambital region (PL 11, figs. 11-13, 

 14-16). The principal and most characteristic row of primary radioles 

 (PL 11, figs. 11-13) is at the ambitus and it is the one which with the pave- 

 ment of abactinal primary radioles gives to Colobocentrotus and Podophora 

 their striking characteristics. These ambital radioles vary in length from 

 15 to 18 mm.; they are olive-green in color. 



It is interesting to follow the gradual changes which take place in the 

 ambital radioles (PL 11, figs 11-13) as they are succeeded by the more 

 abactinal radioles (PL 11, figs. 14-16) and gradually form more pavement- 

 like, hexagonal, somewhat shorter radioles (PL 11, figs. 17, 18), to be followed 

 by still shorter radioles (PL 11, figs. 19-21), and then the irregular, short, 

 mushroom-shaped polygonal or hexagonal radioles (PL 11, figs. 22-24; 25-27 ; 

 28-30; 31-33), on the thirteenth plate counting from the actinostome.- A 

 series of small, mushroom-shaped radioles has also been selected from the 

 ocular and genital plates. They continue the abactinal pavement over the 

 abactinal system (PL 11, figs. 34-36; 37-39; 40, 41; 43, 43; 44, 45). The color 

 of the primary radioles is olive green. It will be observed that with the 

 exception of the radioles of the actinal side and of the miliary spines all 

 the radioles are asymmetrical. 



The Lanterns and Auricles of Colobocentrotus and Podophora. 



Plates 13, figs. 1-4; 14, figs. 5-7; 15; 26, figs. 9-13; 27; 28; 

 42, figs. lU; 43, figs. 4, 5; 44. 



The differences in the various parts of the lanterns of Podophora pedifera 

 and P. atrata are very marked ; they are seen in the shape of the compass 

 (Pis. 15, figs. 13a b ; 27, figs. 14 a h; 28, figs. 11 a b), in the proportions of the 

 corrugations of the sides of the pyramid (Pis. 15, figs. 4, 5, 8, 9 a b ; 27, 

 figs. 4, 5, 7, 8 b ; 28, figs. 4, 5, 7 b, 8 b) ; they are much coarser and less 

 numerous in young specimens (see PL 27, figs. 4, 5, 7, 8). The foramen of 

 the pyramids is longer in P. pedifera than in P. atrata (Pis. 15, figs. 2, 3; 

 27, 2, 3; 28, figs. 2, 3). The foramen formed by the apophyses and their 

 hooklike appendages (PL 15, figs. 3, 4) is much larger than in young specimens 

 of P. atrata (PL 27, figs. 5, 4), where it is rectangular ; there are no hooks to 

 the apophyses (PL 27, figs. 7, 8 a) while they are well developed in older speci- 



