DR. G. J. HINDE ON RECEPTACULITIDA, 847 
Fig. 10. A specimen with a flattened base and depressed summit, showing 
faint vertical and concentric lines formed by the horizontal spicular 
rays. 
Vex A ae showing sections of the vertical rays of the spicules, 
both the spicular plates and the horizontal rays having disappeared. 
The specimens are from the lowest beds of Silurian age in the isle 
of Gotland ; fig. 1 is from Djupvik, and the others from the vicinity 
of Visby. With the exception of fig. 1c, they have been lent by 
Prof. G. Lindstrom from the Royal Museum at Stockholm. 
1 d-g. Showing the characters of the summit-plates of the spicules. 
1d. The upper portion of fig. 1, enlarged twice, showing the regular dis- 
position of the spicular plates and the slightly elevated distal angles 
of those of the zonal region. 
le. Shows the arrangement of the minute spicular plates at the summit 
of a small specimen, surrounding the central aperture. Enlarged 
six times. 
1f. The base of fig. 1, enlarged three times, showing the eight diamond- 
shaped spicular plates of the nucleus and the plates succeeding them, 
each having a clearly marked central spot, indicating the centre of 
the spicule. 
lg isa portion of the lateral surface of a specimen, enlarged four times, 
showing the extension of one of the horizontal rays of each spicule, 
from beneath the distal angle of its corresponding summit-plate, over 
the summit-plate of the spicule in front of it. In the centre of the 
figure are the modified summit-plates developed at the intercalation 
of a fresh row of spicules. 
14-7. Showing the characters of the horizontal spicular rays. 
1h, 1%, are portions of the lateral areas of two specimens in which the 
surface summit-plates have disappeared, showing the four horizontal 
rays of independent spicules. The rays are often incomplete, and 
they frequently overlap each other. Enlarged three times. 
17. The surface of the upper portion of a specimen in which only 
three of the four horizontal spicular rays are preserved ; the fourth, 
or distal ray, having disappeared with the summit-plate. Enlarged 
three times. 
1 £-o. Showing the characters of the vertical spicular rays. 
1%, 1, m are fractured specimens, showing the tapering extension and the 
free termination of the vertical rays in the interior of the central 
cavity, now filled with matrix. Natural size. 
1 is a smooth vertical section, and lo a transverse section, similarly 
showing the extension of the vertical rays. 
Fig. 2. Ischadites Lindstremi, Hinde. 
The base of a specimen showing the ridges formed by the matrix 
between the margins of the spicular summit-plates, which have dis- 
appeared ; the dark spot in the centre of each rhomboidal area indi- 
cates the vertical rays of the spicules ; some traces of the horizontal 
rays are also shown. From Silurian strata at Petesvik, isle of 
Gotland. 
Puate XXXVI. 
Figures 1, la-c. Spherospongia tessellata, Phillips, sp. 
Fig. 1, A specimen, imperfect at the summit, showing the hexagonal spicular 
summit-plates of the surface. Natural size. From Middle Devonian 
strata at Newton Bushell, near Torquay, Devonshire. In the collec- 
tion of the British Natural History Museum. 
