British Species of Sponges. 335 
Microsclera, two :— 
1. Toxa, very slender, with a short, abrupt, spiral curve in 
the middle, the extremities long and straight. ‘The tips are 
generally smooth and very sharp, but in some cases a few 
very minute spines may be detected on the spicule generally. 
These spicules range from *250 up to ‘412 millim. in length, 
the majority measuring between *3 and ‘4 millim., by an 
gretses breadth of only 0015 to 002 millim. (figs. A, 5 and 
F 
There are also a few much smaller toxa, among which are 
some in which the central curve is comparatively large and 
the long straight ends absent (fig. A, 7). These last spicules 
are as stout as the longest; their tips are generally micro- 
spined. Two measured were respectively *091 and -143 
millim. long. 
2. Isochele, of the usual navicular type, minute, ‘017 to 
019 millim. long (figs. A, 9 and 10). 
The columns are composed of the larger kind of styles, 
No. 1, and are sparsely echinated by the entirely spined 
spicules, No. 2. The slender subclavate styles, No. 3, lie 
imbedded in the substance of the sponge, as above stated, 
generally parallel with and near to the surface. The chele 
and toxites are distributed throughout the sponge-substance, 
and do not lie in any particular direction as regards the 
columns or the surface. 
The megasclera of this sponge agree very closely in cha- 
racter with those of the other species of Microciona proper, 
and the chela is of the well-known shape which is character- 
istic of a very considerable number of species in that and other 
genera; the toxite, on the contrary, is of a peculiar and 
striking form, which seems to call for a few remarks. 
In the other species of the genus, and, so far as I have 
been able to ascertain, in all the species (with one exception) 
of similar spiculation in other genera, the toxa lie flat in one 
plane from end to end; here and there perhaps one may be 
found with a barely perceptible twist; but in this sponge I 
have not been able to find one which can be focussed under a 
3-inch objective from end to end at the same time. In the 
long straight-armed form the twist is nearly confined to the 
central sinus, and the conformation of this spicule may be 
roughly imitated by laying a straight piece of wire along a 
lead pencil and taking one turn round the middle ; if then the 
pencil be drawn out and the wire turned on its axis, it will be 
found to present in different positions as regards the eye the 
appearances shown in the figures ot the toxites (figs. A, 5 and 
6). The wire model would differ from the actual form of 
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