remarkable Species of Cliona. 61 
cells left unclosed are those of C. mucronata, while the ones 
shaded with dark lines belong to the next species, C. ensifera. 
Here and there apparently isolated chambers of one or the 
other species occur, as those of C. ensifera at a; these, how- 
ever, are not really isolated, but communicate with chambers 
of the same kind either above or below the plane of the 
drawing. We have now thus brought to light what appears 
to me a very remarkable fact, and one that might easily lead 
to great confusion in species; for no one examining the bur- 
rows in my specimen of Jsis would have supposed them to 
contain two different kinds of sponges. In the outline and 
arrangement of the chambers themselves no difference is to 
be detected ; and but for a little care the different kinds of spi- 
cules within them would certainly have been described as 
belonging to. one and the same species. The necessity for 
' great caution in deciding what spicules to eliminate and what 
to retain in determining the true complement of spicules 
proper to a sponge has already been illustrated by the re- 
searches of Carter, who has had frequently to disentangle the 
spicules of commingled species one by one as it were, and so, 
by immense care, has arrived at correct results where failure 
would otherwise have been certain. 
2. Cliona ensifera (mihi). 
Sponge burrowing in chambers of the same kind as in the 
preceding species. Spicules of three kinds:—1, an acuate 
spicule (Pl. IT. figs. 10, 11), having a straight or curved shaft, 
which is cylindrical in form for a certain distance from the 
globular pin-like head, and then expanding becomes fusiform 
for the rest of its length, and finally terminates in a more or 
less abrupt point: length 0°0095 inch; breadth across the 
head and broadest part of the shaft 0-0006, and across the 
neck (:0002 inch. 2, a slender acuate (PI. II. figs. 12, 13), 
straight or curved; inflated head variable in shape, spherical 
and ellipsoidal; dimensions variable, averaging 0-0075 inch 
in length and 0°0004 in breadth. 38, a minute or flesh-spi- 
cule (Pl. II. fig. 15), with a straight or curved shaft produced 
into a number of unequal conical spines ; length 0-0006 inch. 
Diaphragms in shape and position very similar to those of 
C. mucronata, though slightly more irregular in outline, com- 
posed of ensiform spicules which lie side by side normal to 
the walls. Owing to the fact, however, that these spicules are 
as often curved as straight, they frequently depart from a nor- 
mal position and are arranged obliquely, forming curved radii 
about the axis or centre of the diaphragm. The heads of the 
spicules form the outer surface of the diaphragm as in C. 
