Sponges of Palau, I — BERGQUIST 
151 
is quite removed from all others by its spicula- 
tion. Apart from this all specimens can be re- 
garded as belonging to one variable species. 
The question is, should this be a species of 
Xestospongia or of Neopetrosia ? Either would 
require expanding the generic diagnosis. In ad- 
dition to the basic reticulate structure, the Palau 
specimen from Sta. 100 has large tracts of verti- 
cally aligned spicules up to 275/x wide and is 
thus approaching the type of structure which 
Xestospongia should possess and which is ex- 
emplified in X. vanilla and X. ( Petrosia ) coral- 
loides. This particular specimen is almost stony 
and brittle. However, the differences which sep- 
arate these sponges are only differences of de- 
gree. Spicule tracts are present, but are much 
narrower in the specimens from Sta. 10 and 
Sta. 47, and these specimens although firm and 
brittle, could not be described as stony. 
It is suggested that the definition of Xesto- 
spongia should be rephrased to include sponges 
like the type species, where a distinct reticu- 
late skeleton is present but where accumulation 
of spicules may be so great as to obscure this in 
parts or in all of the sponge except the sub- 
dermal region. Many sponges assigned to this 
genus have a reticulate surface pattern. 
Neopetrosia does not differ in any way from 
Xestospongia as defined above and as under- 
stood by de Laubenfels (1950:49). The only 
species assigned to Neopetrosia to date are Hali- 
clona longleyi de Laubenfels, the type species, 
Neopetrosia pandora from the Palau Islands, 
and Petrosia similis Ridley and Dendy; all three 
Fig. 14. Xestospongia exigua (Kirkpatrick), (i) U pper right, Sta. 100. (ii) Lower left, Sta. 10. (Hi) Lower 
right, Sta. 47. Clathria cervicornis (Thiele), (iv) Upper left, Sta. 220B. 
