374 ~ THE ATLANTIC. [CHAP. Vv. 
upward to a width at the top of 40 mm. A deep cavity passes 
from the upper open end 
down to the stem-like con- 
striction. The outer surface 
of the sponge is raised into 
spiral ridges somewhat as in 
Euplectella, and under the 
ridges are irregularly spiral 
lines of large holes. The in- 
terior of the cup presents a 
very remarkable character, 
which reminds one at once of 
many of the chalk ventricu- 
ie a lites. The inner layer is deep- 
x ‘ : 
ly fluted, thrown into a series 
of alternating vertical grooves 
and ridges, so that the out- 
line of the cavity in a trans- 
verse section is deeply sinuous. 
The substance of the sponge 
throughout is composed of a 
close anastomozing net- work 
of siliceous fibres; toward the 
outside the net-work much re- 
sembles that of Aphrocallistes, 
while on the inner wall the 
structure is trellis-like, and 
the form of the meshes square 
and more regular. The spaces 
of the net-work are crowded 
Fia. 106.— Lefroyella* decora, Wvyvittie THom- P ‘ 
son. Natural size. (No. 56.) with small regular hexactinel- 
* T have associated with this species the name of our kind friend His Excellency 
Major-general Lefroy, C.B., F.R.S., Governor of Bermudas. 
