908 LIVERPOOL BIOLOGICAL SOCIETY. 
same genus, Plumohalichondria plumosa, Carter, having 
previously been obtained at Holyhead.* I found it at 
Puffin Island, April, 1889, and at Hilbre Island, May 
1889, a short way above low-water mark. 
Bowerbank + records it from St. Katherine’s Cave, 
Tenby ; rocks off Hastings ; Guliot Caves, Sark ; Lennen 
Cove, Land’s End, Cornwall, and he describes the external 
appearance of this sponge in the following words :—“ Its 
appearance is that of a small patch from one to two inches 
in diameter, of dark clot of blood adhering closely to the 
surface of the rock, and it can be obtained only by cutting 
away the piece of stone to which it adheres. It rarely 
exceeds about half a line in thickness. Its extreme thin- 
ness readily distinguishes it from the deep red coloured 
sponge, Chalina seriata,§ which occurs abundantly along 
with it in that cave (at St. Katherine’s Island, Tenby), 
and which is so thick as to be easily removed from the 
rock with a knife.” Bowerbank’s description applies very 
well to the condition in which I found this form, together 
with Clathria serrata, at Puffin Island. In order to get 
sections of Plumohalichondria atrasanguinea one has to 
remove a portion of the rock (carbonate of lime) together 
with the sponge, and dissolve the former ‘vith acids. 
Specimens from Hilbre Island are of less use for histologi- 
cal purposes because the rocks there consist of sandstone. 
The ceratose skeleton of our species consists of a limit- 
ing membrane which is closely applied to the rock, and 
of ascending fibres, arising about at right angles from the 
limiting membrane. Those fibres are furnished abundantly 
with echinating megascleres of two kinds; there are styli 
* Thomas Higgin, ‘‘ Report on the Porifera,” in ‘‘ Fauna of Liverpool 
Bay,” p. 78. 
+ Bowerbank, ‘‘ British Spongiade,” vol. i,, p. 139. 
§ Chalina seriata is identical with Clathria seriata, see p. 205. 
