CALCAREA. 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 /u. to 

 950 /n long X 20 jx to 28 ju, thick. Many of these spicules have long 

 flattened areas just below the outei'most liend, looking as if the spicule 

 had licen diverted liy contact with a plane surface. 



There are minute spincd oxea of two types : — 



(b) Straight, refringeut, and thin, 50/x. long x 1 '2 ju, thick. 



(c) Curved, hastate, and thicker, 55 /x long x 4 /x to 5 /x thirlv-. 



The triradiateA are of tw(j sorts : — 



('0 Approximately regular trinidiates from the dermal cortex and body-wall 

 with straight rays, tapering slightly to near their extremities, then shai'ply 

 pointed. The rays and angles are nearly liut not exactly equal. Rays 

 110 /A to 220 /x long X 8 ju, to 12 /A thick. 



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

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

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

 ir,0/x hnig X 12 /x to 14 ;u, thick. Oral angle 120° to 145°. 



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

 sharply pointed, 300 /j. to 500 /x long x 11/x to ]2/x thick. Paired rays 

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

 150°. iVngle of fold very variable, 115° to 100°. Apical ray nearly 

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

 Angle between apical ray and basal ray 165°. 



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

 20 /x thick. 



(//) Straight, strongly hastate, thin, spined oxea forming the fringe, 100 /x to 

 200 /x long X 1 /x to 3 /x 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, 

 SOjix to 90 /x long X 6/x thick. Paired rays equal and bent slightly down, 

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

 5 /x 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 fi, increasing considerably lower down. Thickness 

 7 /x to 9/x. Paired rays equal, straight or slightly liracket-shaped, 110/x 



