THE GENUS COLOBOCENTROTUS. 25 
The ambulacral radioles 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 (PI. 11, figs. 17-13, 
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 17-13) as they are succeeded by the more 
abactinal radioles (Pl. 11, figs. 144-16) 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 (PI. 11, figs. 34-36; 37-39; 40, 41; 42, 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. 1-4; 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 
(Pls. 15, figs. 13 a b ; 27, figs. 14 a b; 28, figs. 11 a 5), in the proportions of the 
corrugations of the sides of the pyramid (Pls. 15, figs. 4, 5, 8, 9 a 6; 27, 
figs. 4, 5, 7, 8b; 28, figs. 4, 5, 7 b, 8b); 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 (Pls. 15, figs. 2, 3; 
27, 2, 3; 28, figs. 2, 3). The foramen formed by the apophyses and their 
hooklike appendages (PI. 15, figs. 3, 4) is much larger than in young specimens 
of P. atrata (Pl. 27, figs. 3, 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- 
