31 



PLATE XII. 



POLYMASTIA MAMMILLARLS, 



Vol. ii, p. 71, ' Mon, Brit. Spongiadse.' 



Fig. 1. A remarkably-fine adult specimen of P. 

 mammillaris from Larne Lough, Ireland, in the state in 

 which it came from the sea, having been preserved in 

 spirit. Natural size. 



Fig. 2. A young specimen of the same species with 

 one fistula only partially developed, in the dried state. 

 Natural size. 



Figs. 3, 4. Young specimens of the same sponge, 

 with the fistula in a more advanced stage of develop- 

 ment, but still incomplete, from dried specimens. 

 Natural size. 



Figs. 5, 6. Two of the fusiformi-spinulate, skeleton 

 spicula. X 123 linear. 



Fig. 7. The basal portion of one of the fusiformi- 

 enormi-spinulate, skeleton spicula. X 250 linear. 



Fig. 8. -The basal portion of a bispinulate, skeleton 

 spiculum. X 250 linear. 



Fig. 9. One of the skeleton spicula in an early stage 

 of development, showing the prominent spinulation of 

 its base. X 250 linear. 



Fig. 10. A portion of the external surface of one of 

 the adult fistula near its distal termination, exhibiting 

 portions of two of the primary fasciculi of the skeleton, 

 the transverse bands of secondary skeleton spicula, 

 and the radiating fasciculi of external defensive spicula, 

 from a specimen in Canada balsam. X 80 linear. 



Fig. 11. One of the small, fusiformi-spinulate, 

 external defensive spicula. X 123 linear. 



