BRITISH SPONGIAD^l. 71 



7. Polymastia mammillaris, Bowerbank. 



Sfongia penicillus, Montagu. 



HaLICHONDRIA MAMMILLARIS, Johnston. 



Sponge. Massive, sessile. Surface even, hispid. Oscula 

 terminal, congregated on slender mammasform cloacal 

 fistulas ; rarely simple. Pores inconspicuous. Dermis 

 of the basal mass sub-crustular. Dermal membrane 

 pellucid, aspiculous. Dermis of the cloacal fistulas 

 furnished abundantly with radiating fasciculi of 

 secondary external defensive spicula ; spicula based on 

 the external surface. Skeleton. Fistulas numerous, 

 strap-shaped, frequently truncated, or somewhat ex- 

 panded at their distal terminations. Spicula of the 

 primary fasciculi fusiformi-enormi-spinulate, rarely 

 fusiformi-acuate, long and stout. External defensive 

 spicula of basal mass, same as those of the skeleton. 

 External defensive spicula of fistulas fusiform i-spinu- 

 late, short and small, very numerous ; congregated in 

 radiating fasciculi, and based on the dermal mem- 

 brane. Tension spicula fusiformi-spinulate, variable 

 in size. 



Colour. Light ochreous yellow. 



Habitat. Larne Lough, Mr. Hyndman ; Guernsey, 

 Rev. A. M. Norman ; Shetland, Mr. Barlee ; Orkney 

 Islands, Capt. F. W. L. Thomas, R.N. 



Examined. In the fresh and dried states. 



I am indebted to my friend, Mr. George Hyndman, of 

 Belfast, for two fine specimens of this species, each about 

 two and a half inches in diameter, and about half an inch 

 in thickness. Both have the appearance of having coated 

 water-worn stones. The cloacal fistulas are very abundant 

 on both specimens ; their average length is about six or 

 seven lines, and their width a line and a half; they are 

 compressed for the whole of their length, and the distal 



