24 
Mr. W. J. Sollas on a new Genus and 
(fig. 3, 3 ) • if accompanied by increased concentric growth of 
the initial cell, then the pin-headed acuate (fig. 3, 4 ) is pro¬ 
duced. 
4. An elongation of the cell in two directions inclined to 
each other at a less angle than 180°, gives us the curved 
acerate (fig. 3, 5), which is both biradiate and biaxial. 
5. The inclination of the two rays in fig. 3, 5 , is followed 
by the appearance of a third in fig. 3, 6, where we have the 
triradiate spicule of Plectronella. In this spicule two of the 
radii arise from the proximal face of the cell and grow inwards 
towards the axis of the fibre on which it is situated, and the 
third ray arises distally and grows outwards away from the 
axis. 
6. A growth of the cell in three directions making equal 
angles with each other, and having no determinate relations 
to any symmetrical line within the sponge, gives us the equi¬ 
angular triradiate spicule (fig. 3, 7), which occurs abnormally 
in Dercitus Bucklandi. (Triradiate spicules also occur as 
varieties in Eccionema , Bw T k., and Normania , Bwk. ( l Mono¬ 
graph of British Spongiadge,’ vol. iii. pi. ix. figs. 4, 5, and 
pi. lxxxi. figs. 6, 8), and as a normal form in Sphinctretta 
horrida (Schmidt, ‘ Spongien d. atlant. Gebietes,’ pi. vi. fig. 7) 
and in Pachastrella connectens.) 
7. A quadriradiate growth of the cell in directions having 
no determinate relations to the form of the sponge gives us 
the normal spicule of Dercitus Bucklandi (fig. 3, s). 
