26 
Mr. W. J. Sollas on a new Genus and 
that a spur-like spicule is found wholly inside the fibre of 
Plectronella. 
If there were no spur-shaped spicules in Plectronella , the 
projection of its acerate spicules beyond the surface of the 
fibre would place it in the Axinellid family; but since they are 
present and characteristically seated on the fibre, its proper 
place is clearly enough with the Ectyonida, amongst which it 
will take rank, on account of the unique form of its echinating 
spicule, as the representative of a distinct group, the Plectro- 
nina. 
Order ECHINONEMATA, Carter. 
Family Ectyonida, Carter. 
Group Plectronina , Sollas. 
Genus Plectronella. 
Species Plectronella papillosa, Sollas. 
EXPLANATION OF THE PLATES. 
Plate IV. 
Plectronella papillosa. 
Fig. 1. The entire sponge, seen from above. \ natural size. 
Fig. 2. Sponge seen from below. \ natural size. 
Plate V. 
Plectronella papillosa. 
Fig. 1. Acerate spicule from the interior of the fibre. 
Fig. 2. Spur-shaped spicule (when in situ echinating the fibre). 
Fig. 3. Flesh-spicule. (Figs. 1-3 all drawn to the same scale, ^y 2 .) 
Fig. 4. Flesh-spicules, straight and curved. 
Fig. 5. A sheaf of flesh-spicules. (Figs. 4 & 5 x 400). 
Figs. 6-10. Varieties of the acerate spicule (x 140). Fig. 6 a form fre¬ 
quently assumed when the acerate spicule projects from the 
fibre echinately. 
Fig. 11. Two acerates ankylosed together ; ends broken. 
Figs. 12, 13. Bifurcated acerate spicules, x 140. 
Fig. 14. Young form of echinating or triradiate spicule. X 140. 
Fig. 15. Variety of acerate. X 140. 
Fig. 16. A spicule not belonging to the sponge, but met with in its 
examination ; it presents a cylindrical shaft terminated at each 
end by a microspined globular head, x 315. 
Fig. 17. Biradiate uniaxial variety of echinating spicule. 
Fig. 18. Similar variety, showing axial canal. 
Fig. 19. Biradiate biaxial variety ; rays inclined at 90° to each other. 
Fig. 20. Simil.ar variety but with single smooth ray taking the same 
direction as it would if its fellow were present. 
Fig. 21. Normal form of echinating spicule. (Figs. 17-21 X 315.) 
