334 Mr. A. Hancock on the Excavating Powers of Sponges, 
enlarged extremity; and sometimes the poimted end is a little 
recurved, giving to the spiculum a slight S-like twist. 
This species is common on the coast of Northumberland, where 
almost every piece of limestone at low-water mark has the sur- 
face riddled by it : it likewise occurs in the shell of Fusus antiquus 
and Buccinum undatum. I have obtained it also in oyster-shells 
from Prestonpans. The walls of the burrows of this form are 
strongly punctured, and every here and there are drilled with 
small conical holes. When in the thin shell of Fusus or Bucci- 
num, the branches are all confined to the same plane, and then 
this species has considerable resemblance to a Gorgonia. But 
when it takes up its abode in limestone, the branches frequently 
pass vertically to some depth into the substance of the rock, 
giving to the sponge a very complicated structure. 
In old specimens the branches become less regular, increasing 
much in thickness and number until very small spaces divide 
them: the external walls are now liable to give way, and the 
sponge being thus exposed must either perish or sink deeper 
into the matrix. 
C. radiata. Pl. XV. fig. 3. 
Sponge delicately branched in a radiating manner; the branches 
being ;4,th of an inch thick and divided at unequal distances into 
elongated lobes: terminal twigs simple, minute, linear : papillee 
rather variable in size, frequently very small, placed in a single 
close-set row along the branches ; in the central axis where the | 
branches unite there is one much larger than the rest. Spicula 
gith of an inch long, stout, straight, frequently a little bent ; one 
end with a large ovate head widest at its junction with the shaft, 
which is a little constricted at the point of union, and from which 
it is strongly defined by a dusky shadow. . 
This form buries itself in the shell of Triton variegatus, and is 
easily recognized on the surface by the radiating lines of minute 
close-set papillary punctures. It is very destructive to the shells 
it attacks: at first it is composed of a few simple radiating 
branches ; these afterwards enlarge, and send off lateral shoots 
which anastomose with the adjoining branches, and ultimately 
fuse, as it were, towards the centre, which becomes one mass of 
sponge frequently an inch wide; all the shell, of course, at this 
part being entirely removed. 
C. gracilis. Pl. XIV. fig. 7. 
Sponge composed of a few long, slender, linear branches, rarely 
if ever anastomosing, extending in length upwards of 5 inches, 
and only ;4,th of an inch thick, with a few distant, imdistinet 
constrictions indicating an approximation to a lobed structure: 
