PLATE XVII, 
Transverse sectio ns of Echinoid Radioles. 
452. « Cidaris » trigona, from St. Cassian (Brit. 
Mus., E 10101); the flattened face is upper¬ 
most; the axis of the radiole lies at the 
lower right-hand corner of the figure; X 30 
diam. 220 [ 
Pag. 
453. « Cidaris » linearis, from St. Cassian (Brit. 
Mus., E 10102); the position of the axis 
is marked by a cross ; X 60 diam. . . . 227 
All figures were drawn from the sections by G. T. Gwilliam, under the Author’s direction, at a magnification 
of 80 and 40 diameters, respectively, and were reduced by photography to the present scale. 
