THE GENUS COLOBOCENTROTUS. 1g: 
than those of that species (Pls. 33, figs. 1-3; 37, figs. 1-3). The primaries of 
the abactinal side of the test are much smaller than those of Podophora 
and are loosely packed upon the test, leaving considerable open space round 
each tubercle. This open space is specially marked on the line separating the 
ambulacral from the interambulacral zones (Pls. 33, figs. 2, 3; 37, figs. 2, 3). 
The general color of the radioles is of a grayish pink color with a slight 
tinge of green on the upper surface of the larger primary ambital radioles. 
Seen in profile and from the abactinal side the primary radioles which are 
irregularly circular at the tip are seen to diminish very gradually in size above 
the ambitus as they reach towards the apical system (Pls. 33, figs. 2, 3; 37, 
figs. 2, 3). The large abactinal radioles immediately above the ambitus are 
arranged more closely than those more distant from it (Pls. 33, fig. 3; 37, 
fig. 3). 
Seen from the actinal side (Pls. 33, fig. 1; 37, fig. 1), the actinal membrane 
is nearly bare, carrying but few small clusters of miliary spines on the pairs 
of poriferous plates and a few minute spines irregularly scattered over it. 
(Pls. 33, fig. 1; 37, fig. 1). The actinal side of the test below the ambitus is 
covered with slender somewhat club-shaped spines varying but slightly in 
shape or size between the actinal system and the actinal side of the ambitus. 
The poriferous fields are separated by wide interambulacral zones (Pls. 33, 
fig. 1; 37, fig. 1). 
The spines of the actinal system close to the teeth are short, club-shaped, 
slightly flattened (Pl. 40, fig. 1); those from the buccal membrane are some- 
what longer (PI. 40, fig. 2). Half way between the actinal system and the 
ambitus the radioles are much stouter and only slightly club-shaped (PI. 40, 
figs. 3, 4), as are the smaller spines found on the smaller secondary granules 
or larger miliaries (Pl. 40, fig. 5); these spines are all delicately striated with 
an ill-defined milled ring. 
Below the ambitus we pass suddenly to much larger flattened, angular 
radioles, rounded at the tip, with a large base for the muscular attachment 
(Pl. 40, figs. 6-8). These spines form a part of the principal subambital 
fringe of radioles, the primary radioles of which are figured on Pl. 40, 
figs. 9-11; these radioles resemble those of P. pedifera, but are comparatively 
shorter and narrower; they are flat on the lower surface, somewhat spathi- 
form on the upper surface, and greatly flattened towards the tip of the 
radiole, as is shown by a profile view (Pl. 40, figs. 9, 11). 
We now come to the larger spines of the abactinal pavement immediately 
