Dr. G. J. Hinde on Fossil Calcispongie. 205 
Fig. 25. Corynellarugosa. Spicule of the fibre. Sagittal triradiate, with 
straight lateral rays. 
All the above figures are drawn by means of the camera lucida, and 
magnified to the same scale of 200 diameters. 
PLATE XII. 
4g. 1. Longitudinal microscopical section of a portion of the fibre of 
Sestrostomella rugosa, as seen by transmitted light, showing one 
ray of a relatively large tri- or quadriradiate spicule in the 
centre (a), and the bisected outlines of sagittal and irregular 
triradiate spicules (6), which are confusedly intermingled to- 
gether to form the fibre. 
Fig. 2. Transverse section of the same, showing a cross section of one 
ray of a large central spicule (a), and the cut edges of the smaller 
triradiates surrounding it. ‘The finer lines near the margin of 
the fibre in this and the preceding figure are probably out- 
lines of minute spicules, so compactly wedged together in the 
fibre that the individual forms cannot be distinguished. 
Fig. 3. Sestrostomella rugosa. Fragment of a large triradiate spicule, 
showing portions of the three rays, from the interior of the fibre, 
as seen in a microscopic section, 
Fig. 4. The same. Fragment of triradiate spicule with unequal arms. 
Fug. 5. The same. Fragment of quadriradiate spicule. 
fig. 6. The same. Triradiate (fork-shaped) spicule with irregular and 
unequal arms. 
Fig. 7. The same. Irregular quadriradiate spicule. 
Fug. 8. The same. Sagittal triradiate (pickaxe) spicule, with the lateral 
rays (imperfect) curved towards the basal ray. 
Figs. 9-11. The same. ‘Triradiate spicules, the rays incomplete. 
Figs. 12-15. The same. Triradiate (fork-shaped) spicules from the fibre, 
showing the elongate basal ray and the lateral rays, often slightly 
unequal in length, and curved backwards, so as to become nearly 
parallel with each other. 
Fig. 16. Sestrostomella clavata. Portion of large quadriradiate spicule, 
showing the imperfect sinuous facial rays and the truncated 
base of the apical ray, from a microscopic section of the fibre. 
The irregular lines within the spicule are apparently fractures 
in its substance. 
Fig.17. The same. Quadriradiate spicule (@mperfect) similar to but 
smaller than the preceding. 
Fig. 18. The same. Triradiate spicule. 
Fig. 19. The same. Portion of a minute quadriradiate spicule. 
Figs. 20, 21. The same. Fragments of irregular triradiate (fork-shap=d) 
spicules. 
Figs. 99-94. The same. ‘Triradiate (fork-shaped) spicules, showing slight 
variations in size and form. 
Fig. 25. The same. ‘Triradiate(?) spicules, subregular in form, from a 
small smooth portion of the exterior surface of the sponge, pro- 
bably the part from which the growth of the sponge commenced. 
x 150. 
With the exception of tig. 25, all the above are drawn from microscopic 
sections by means of the camera lucida, and magnified to the same scale 
of 200 diameters. 
