new Recent Pharetronid Sponges. 507 



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

 a thick pile on the surface of the chinniey, 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 fju long, I'b fi thick. (/>) (PI. XIV. fig. 8) 

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

 bayonet end, 234 [x long, 3*8 yu. 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. tigs. 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 //-; the prongs are 

 about 25 yu. 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 Sjncules. — (1) triradiates (PI. XIV. fig. 12) with 

 unpaired ray longer than paired, tapering, and then slightly 

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

 curved, 49 fi 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-ty^Q in fossil 

 Pharetrones. 



(2) Qiiadriradiates (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 /* long 

 and only 5 /a 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 ; tliis 

 latter kind also becomes cemented with the framework in this 

 region. 



The body of the skeleton is formed of thick quadriradiates 



