CALCAEEA. 43 



usually slightly bent to the opposite side from the outer end, giving the 

 spicule an S shape. The outer end is slightly swollen and roughened. 

 The thickness varies very irregularly throughout the length, 550 yu, to 

 950 /A long X 20 fi to 28/a thick. Many of these spicules have long 

 flattened areas just below the outermost bend, looking as if the spicule 

 had been diverted by contact with a plane surfac^. 



There are minute spined oxea of two types : — 



(6) Straight, refringent, and thin, 50;ia long x 1 -2 /a thick, 

 (c) Curved, hastate, and thicker, 55 /a long x 4 /a to 5 /^ thick. 



The triradiates are of two sorts : — 



{d) Approximately regular triradiates from the dermal cortex and body-wall 

 with straight rays, tapering slightly to near their extremities, then sharply 

 pointed. The rays and angles are nearly but not exactly equal. Eays 

 1 10 |u, to 220 /A long x 8 /x to 12 //, thick. 



{e) Large alate triradiates from the body-wall. Basal rays straight, tapering 

 moderately, then fairly sharply pointed, 400 /a to 500 /u, long x 12 /a to 

 14 /A thick. Paired rays nearly straight, tapering,^ then sharply pointed, 

 160 /A long X 12 /x to 14 /A thick. Oral angle 120° to 145°. 



(/) Chiactines. Basal rays straight, tapering slightly to near the end, then 

 sharply pointed, SOO/tto 500/i, long x 11/* to 12)ti thick. Paired rays 

 straight, 120/* to 160 /i long x 10/* to 12/* thick. Oral angle 115° to 

 150°. Angle of fold very variable, 115° to 160°. Apical ray nearly 

 straight, sharply pointed, 100/* long x 8/* thick. Set-off moderate. 

 Angle between apical ray and basal ray 165°. 



Oscular spicules. — Near the oscule type (a) spicules get smaller, 330 /i long x 

 20 /* thick. 



{g) Straight, strongly hastate, thin, spined oxea forming the fringe, 100 /i to 

 200 /* long X 1 /* to 3 /i thick. The spear-head is swollen at the junction 

 and very sharply pointed. These spicules are also found in the oscular 

 collar a short distance below the edge lying tangentially and occasionally 

 projecting. 



(A) Small quadriradiates from the oscular edge. Basal ray straight, pointed, 

 50 /* to 90 /I long X 6 /* thick. Paired rays equal and bent slightly down, 

 30 /* to 60 /* long X 5 /(- thick. Apical ray straight, pointed, 20 /i long x 

 5 /* thick. Oral angle 160°. 



(^') Large quadriradiates lining the oscular collar. Basal ray straight, tapering 

 uniformly to a fine point, sometimes bent backwards in side view. Length 

 near oscular edge 200 jx, increasing considerably lower down. Thickness 

 7/0 to 9/*. Paired rays equal, straight or slightly bracket-shaped, 110 /i 



