new Recent Pharetronid Sponges. 507 



(3) Monaxons. Three kinds : (a) (PI. XIV. fig. 7) forming 

 a thick pile on the surface of the chimney, and arranged 

 vertically to the long axis or pointing obliquely upwards ; 

 the spicules are straight, anisoactinate, thick and spined in 

 proximal half, but tapering gradually to a fine, smooth, 

 bayonet end, 87 /x long, 7'5 ft thick* (/>) (PI. XIV. fig. 8) 

 a longer kind, straight, smooth or strongly spined, with distal 

 bayonet end, 234 fi long, 3*8 //. thick, situated at upper end 

 of pore-chimney, (c) Very slender fringe spicules (PI. XIV. 

 fig. 9), long, curved, and with very fine distal end. 



(4) Tuning-forks (PI. XIV. figs. 5, 6) in the hard basal part 

 of the pore-chimney. The shaft is smooth and with a club- 

 shaped proximal end, the length being 133 /x; the prongs are 

 about 25 /x long ; fig. 6 shows a rare kind with prongs widely 

 apart ; occasionally a fourth " ray " is present (fig. 5) . These 

 spicules are without definite orientation ; sometimes the shaft 

 points to the lumen of the poral or oscular tubes, sometimes 

 the prongs; or, again, the spicules may lie parallel to the 

 axis of the chimneys. 



Oscular Spicules.— (I) triradiates (PI. XIV. fig. 12) with 

 unpaired ray longer than paired, tapering, and then slightly 

 swelling to distal end, 104 /x long, 5 /x thick; paired ray 

 curved, 49 /x long. Unpaired angle 150°. Another kind 

 (fig. 13) with nearly equal rays, and a third kind (fig. 14) 

 with the third ray much reduced and approaching in character 

 what Dr. Hinde (2. p. 160) calls the Corynella-Xy^Q in fossil 

 Pharetrones. 



(2) Quadriradiates (PI. XIV. fig. 10), of the same general 

 character as the oscular triradiates, but with relatively longer 

 paired rays. 



(3) Monaxons (PI. XIV. fig. 16) forming a thick pile on 

 the surface of the chimney, considerably thicker than in the 

 case of the poral chimneys. These spicules are 200 /x long 

 and only 5 /x thick, straight, finely spined in middle region, 

 usually terminating distally in a bayonet point, but some- 

 times with a straight end. 



(4) Tuning-forks (PI. XIV. fig. 15). 



The thick hard basal part of the poral and oscular tubes is 

 composed of thick-rayed tri- and quadriradiates with pointed 

 or sometimes rounded rays, cemented together, and with the 

 gastral ray or odd ray pointing in to the lumen (PI. XV. 

 fig. 4). Figs. 5, 6, 7 show young separate tri- and quadri- 

 radiates, and fig. 8 a stout monaxon with thick spines; this 

 latter kind also becomes cemented with the framework in this 

 region. 



The body of the skeleton is formed of thick quadriradiates 



