BRITISH SPONGIAD^l. 215 



on any part of the dermal membrane, which is continued 

 without fracture from the extruded portion deep into the 

 body of the sponge, while, on the contrary, the mammil- 

 lated plug spoken of by Dr. Johnston, has not a single 

 speculum embedded in or on its membranes, and is totally 

 detached from the neighbouring sponge tissues. It is very 

 similar in form to the oscular portion of the sponge, but 

 this is the only similarity that exists between them ; and it 

 is abundantly evident that this body is simply the remains 

 of one of the lithodomus Annelids which probably excavated 

 the tortuous passages which have subsequently been taken 

 possession of by the sponge. The plug consists of a cir- 

 cular thickened membrane with a central orifice or depres- 

 sion, equal to about one third of its whole diameter. 

 Within this area there is a membrane of a deep blood-red 

 colour. The outer portion of the surrounding membranous 

 ring is thickly studded with mammillae, nearly all of which 

 are pear-shaped, the smaller end being the distal one, and 

 the whole present every appearance of being the tentacles 

 of an Annelid in a state of complete retraction. 



The learned author of the ' History of the British Sponges' 

 has also described two varieties of his Halicltondria celata. 

 The first as " massive and rude." The second as " sinuous, 

 the shape dependent on the form of the holes in old oyster 

 shells, which the sponge occupies and fills." The latter 

 variety is Cliona celata of Grant ; the former now consti- 

 tutes the type of my genus Uaphyrus. When Dr. Johnston 

 was writing the histor} r of H. celata, he sent to me for 

 examination, as he states in his work, " some morsels" of 

 the sponge, requesting my opinion regarding the spicula, 

 camera lucida drawings of which I sent to him, and which 

 he has figured in page 127 in his work. I had not, at that 

 time, seen a complete specimen of Uaphyrus, and it is not, 

 therefore, surprising that either Dr. Johnston or I should 

 have mistaken the spicula of one species for those of the 

 other, as their structure and proportions so closely resemble 

 each other as to render it impossible to distinguish between 

 the two by the normal forms of the spicula alone ; the only 

 guide to distinction that a practised eye would find, would 



