22 PERCY SLADEN TRUST EXPEDITION 
The spicules (Plate 4, figs. 4, 5), may conveniently be grouped in eight categories, as 
follows :— 
(1) ‘Triradiates of the dermal cortex; typically sub-equiangular and equiradiate, 
with centre of spicule slightly uplifted out of the facial plane ; rays fairly stout, gradually 
sharp-pointed, measuring say about 0°22 by 0°02 mm. at the base, but variable. 
(2) Triradiates of the articulate tubar skeleton; markedly sagittal, with widely 
extended oral rays; rays nearly straight and gradually sharp-pointed. In a typical 
example, from about the middle of the chamber layer, the paired (oral) rays measured 
about 0°15 by 00146 mm. and the basal ray about 0°27 by 0°012 mm. 
(3) Subgastral sagittal quadriradiates; markedly sagittal, with widely extended 
oral rays, and long, slender, centrifugally directed basal ray, all gradually and sharply 
pointed and remarkably straight, except for the usual bending of the oral rays out of the 
facial plane in accommodation to the shape of the chambers or exhalant canals; with 
minute, very slender, apical ray, vestigial or sometimes (?) absent ; paired rays measuring 
about 0°146 by 0°01 mm.; basal ray about 0°345 by 0°01 mm. 
(4) Quadriradiates of the gastral cortex; large and stout, with gradually sharp- 
pointed facial rays which may or may not be differentiated sagittally, and with very 
strongly developed apical ray, usually curved and gradually sharp-pointed, sometimes as 
large or larger than the facial rays. In a fairly typical example all four rays measured 
about 0°27 by 0°02 mm. 
(5) Triradiates and quadriradiates of the oscular collar; very strongly sagittal ; 
paired rays extended almost in a line with one another, nearly straight, gradually and 
sharply pointed ; basal ray much longer and more slender than the paired rays, straight, 
gradually and finely pointed. In a typical triradiate the paired rays measured about 
0:25 by 0°01 mm., and the basal ray about 0°62 by 0:0083 mm. The orally directed 
apical ray, when developed, is rather short, straight or nearly so, gradually and sharply 
pointed, and measures about 0°075 by 0:0063 mm. 
(6) Quadriradiates of the exhalant canals; these are much smaller than the gastral 
quadriradiates ; their oral rays are usually considerably longer than the centrifugally 
directed basal ray, and curved around the exhalant canal; the apical ray is very slender, 
nearly straight, and all the rays are sharply pointed. The dimensions vary considerably ; 
im a typical case the basal ray measures about 0°05 by 0:006 mm. ; the paired rays about 
0:07 by 0:006 mm., and the apical ray about 0:025 by 0°003 mm. 
(7) Large oxea; nearly straight, fusiform, gradually and sharply pointed, nearly 
symmetrical but sometimes with a slight indication of hastate pointing at the outer end ; 
occurring in the oscular collar and projecting from the dermal surface with their inner 
portions deeply imbedded in the chamber layer; outer ends generally broken off; a 
complete example of about average size measured 2°6 by 0°04 mm. 
(8) Microxea; straight or slightly curved, slender, sharp-pointed at both ends, 
hastate, with a slight enlargement about + of the total length from one end; size about 
0:09 by 0-003 mm. (in the thickest part); observed only on the gastral surface, and there 
only in small numbers. 
