HYMEDESMIA. 57 



prostrate, attenuato-acuate, entirely spined defensive 

 spicula. Internal defensive spicula stout and variable 

 in length, numerous ; retentive spicula arcuate, bi- 

 dentate, equi-anchorate, slender, very numerous, and 

 minute. 



" Colour. Dried state, amber yellow. 



" Habitat. Birterbuy Bay* and Roundstone Bay, 

 County Galway, Ireland ; Rev. A. M. Norman. 



" Examined. In the dried state. 



" This sponge coats very thinly a portion of the inner 

 surface of a fragment of a valve of a Pecten, upon 

 which numerous cells of a Lepralia have been built, 

 and covering a portion of these, and upon parts of the 

 smooth surface of the shell the sponge has been 

 produced. The surface is more or less uneven, but 

 this character of the sponge is probably in a great 

 degree dependent on the extraneous materials based 

 on the shell beneath it. A portion of the sponge 

 covers the dead' cells of the Lepralia, while another 

 portion is based on the smooth surface of the shell, 

 and this assumes the form of a thin equable stratum of 

 sponge. The portion covering the Lepralia had 

 evidently been built over it while it was in a living 

 state ; as upon reversing the mounted specimen nume- 

 rous defensive spicula were seen projected through 

 the basal membrane towards the cells of the Lepralia, 

 evidently as a protection against any assaults on its 

 basal substances ; but where the sponge was based on 

 the smooth surface of the shell no defensive spicula 

 were projected through the basal membrane, but on 



* This and Rovmdstone Bay are two branches of the same inlet on 

 the north side of Galway Bay. I take the spelling " Birterlmy " from 

 the Admiralty chart, but it is also sometimes spelt Birterbie, Birterby, 

 Birterbey, and Bertraghboy. N. 



