346 Mr. A. Hancock on the Excavating Powers of Sponges, 
stomosing; the meshes frequently more than jth of an meh 
wide; lobes elliptical, about 4th of an inch broad, and giving 
off numerous, minute, linear twigs: terminal branches dividing 
dichotomously and furnished on all sides with twigs similar to 
those of the lobes: the dichotomous arrangement may be traced 
throughout the branches. Siliceous bodies of the surface very 
numerous, measuring ;+ th of an inch long and g4,th of an 
inch broad, composed of two whorls, each comprising six or 
seven squarish nodules ; the whorls being placed a little apart 
from each other near the ends of a stout central axis which ter- 
minates at each extremity in a nodule like those of the whorls. 
This is one of the largest and most beautiful of the excavating 
sponges ; only one individual has occurred: it is buried in the 
substance of a large valve of Meleagrina margaritifera which has 
been in my collection many years. The branches extend from 
side to side of the shell, and reach from the beak almost to the 
ventral margin; measuring in length six or seven inches. The 
outer surface of this valve has unfortunately been removed, and 
the papillary punctures consequently destroyed : the ramifications 
of the lobed branches, however, are completely exposed, so that 
they can be traced throughout. But a considerable number of 
the terminal twigs remain imbedded in the shell, and are distinctly 
seen through the mner transparent layer. 
The puncturing of the walls of the cavities of this species is so 
strong that it may be seen even with the naked eye; and they 
are likewise penetrated with numerous small orifices for the 
passage of the minute twigs which come from the underside of 
the lobes. Whether similar twigs pass from the upper surface 
I have not been able to determime, on account of the destruction 
of the external portion of the shell. Those from the lower sur- 
face puncture the innermost layer of the valve; and as pearly 
matter has accumulated around each orifice, the inside of the 
shell is ornamented with numercus clusters, corresponding to 
the lobes, of minute pearl-like points, the beauty of which has 
probably led to the preservation of the shell. 
T. bulbosa. Pi. XII. fig. 10. 
Sponge composed of a few large, irregularly shaped, and 
somewhat depressed lobes, occasionally inclining to square, but 
always more or less rounded; united by a slender stem mostly 
flattened and variable in form : papillz not large, few, penetrating 
the surface of the matrix without order ; apparently not more than 
one or two from each lobe. Siliceous bodies of the surface like 
those of T. cactoides, but a little less. In addition to these bodies 
the surface is provided with triradiate and quadriradiate spicula, 
the rays, measuring 33rd of an inch long, are straight, diverge 
