Dr. G. J. Hinde op ast Calcispongic. 199 
this respect, the condition of the sponge is very favourable for 
the preparation of thin sections. In a transverse section, 
taken from the basal portion of a specimen, examined by 
transmitted light, the fibres appear as bright translucent 
bands from ‘2 to ‘41 millim. wide, in a brownish calcareous 
matrix. The outlines of the spicules appear as very fine lines. 
Where the plane of the section intersects the fibre in the 
direction of its length, it appears as a broad band with well- 
defined margins; when the fibre is cut transversely, the section 
is circular. The fibre exhibits an altogether different charac- 
ter in the form and arrangement of the component spicules from 
that which prevails in the examples of Vertic7llites and Cory- 
nella, already described. Instead of a regular disposition of 
parallel filitorm spicules, nearly uniform in thickness and 
length, the fibre of this species is composed of spicules very 
variable in form, and ranging in size between very large and 
very small forms. A fragment of the fibre and different 
forms of the spicules are represented in Pl. XII. figs. 1-15. 
As these figures are drawn with the camera lucida on the same 
scale of 200 diameters, an idea may readily be formed of the 
variation in size of these spicules. The central portion of the 
fibre generally appears to be occupied by a large tri- or quad- 
riradiate spicule, one ray of which extends along the central 
axis of the fibre, as shown in fig. 1 @ and in section fig. 2 a. 
Sometimes but a single ray of this central spicule is visible in 
the plane of the section; in other instances portions of three 
rays are visible, as in fig. 3. ‘The largest ray of these central 
spicules which I have met with is °d millim. in length and 
‘05 millim. in thickness. Beyond this centrally-placed large 
spicule the remaining portion of the fibre appears to be com- 
posed of several different forms of triradiate spicules, whose 
rays are so compactly and intricately interlaced together that 
it is extremely difficult to ascertain their complete forms with 
any degree of precision. Of those recognizable, some appear 
to be sagittal tri- and quadriradiates, figs. 16, 5, 9-11, with 
rays from :03 to °06 millim. in length; others pickaxe in 
form (fig. 8), or rudely fork-shaped with wide irregularly 
curved prongs (fig. 6); whilst others are regularly fork- 
shaped (figs. 12-15), with short, slightly-curved lateral rays 
and a slender, straight, tapering basal ray, varying in total 
length between -O7 and -19 millim. ‘These spicules appear to 
be distributed in the fibre without any definite order; in a 
few instances, however, I have noticed the small regular fork- 
shaped spicules, with their prongs or lateral rays directed 
towards the margin of the fibre and the basal ray penetrating 
inwards; but this disposition does not appear to be constant. 
