with descriptions of new Species. 347 
at various angles, and each tapers gradually to a fine point ; at 
the place of junction there is generally a slight swelling. 
Several individuals of this species are buried in the specimen 
of Tridacna gigas so often mentioned. In some of them the lobes 
attain a great size, measuring half an inch in diameter. The walls 
of the chambers are much more minutely punctured than in 7. 
cactoides ; and in one of the specimens examined the spicula differ 
from those above described. In the specimen alluded to they are 
multiradiate and triradiate of a peculiar character, the latter, 
Pl. XIII. fig. 8, having one of its rays cut short—little more 
than a squarish tubercle indicating the point of union: the other 
two rays bend from each other rather abruptly near the middle 
and afterwards taper gradually to fine points. The multiradiate 
spicula, Pl. XII. fig. 11, are about three times the length of 
the nodulous bodies, and are rare and very complicated : they are 
formed of two whorls of six or more rays each, the whorls being 
placed rather near together on a central axis which is much pro- 
duced at the ends ; the rays are straight, and, tapermg gradually 
to sharp points, have generally a rounded swelling near the ex- 
tremity. 
I have not yet been able to determine whether the specimen 
provided with these curious spicula is distinct or not, though I 
am inclined to believe that it is. 
EXPLANATION OF PLATES XII. XIII. XIV. ann XV. 
Pirate XII: 
Fig. 1. A portion of the surface of Cliona celata as seen in the compressor, 
magnified about 400 diameters, exhibiting crystalline bodies. 
2. Large crystalline bodies from the same more highly magnified. 
3. Small crystalline bodies also from the same, highly magnified. 
4, Chambers of C. lobata exposed by removing the surface of the ma- 
trix :—one half larger than nature :—a, papillary punctures. 
5, 5. Portions of C. dendritica four or five times the size of nature, ex- 
hibited as seen through the transparent substance of the matrix. 
6, 6. Spicula of C. purpurea much enlarged: a, a spiculum still more 
highly magnified. 
— 7,7. Spicula of C. rhombea much enlarged. 
— 8. Ditto C. lobata ditto. 
— 9. Ditto  C. millepunctata ditto. 
10, a, Crystalline nodulous bodies from the surface of Thoosa bulbosa ; 
b, triradiate and quadriradiate spicula from the same. 
— 11. Maultiradiate spicula from the surface of Thoosa bulbosa?: a, an end 
view of a spiculum ; 4, one of the rays more highly magnified. 
Puate XIII. 
Fig. 1. A portion of the branches and terminal twigs of Thoosa cactoides of 
the natural size. 
— 2. a, A portion of the surface of the same magnified about 200 diame- 
ters, exhibiting nodulous crystalline bodies ; 6, two of these bodies 
more highly magnified. 
