11 



PLATE V. 



Leuconia nivea, Grant. 



Vol. ii, p. 36, ' Mon. Brit. SpongiadEe;' vol. i, pi. xxviii, figs. 351, 352. 



The external characters of this species vary to a very 

 considerable extent in different localities. Exposed to 

 the full action of the sea on the under surfaces of thin 

 ledges of rock, as at the neighbourhood of Scarborough, 

 it appears as a thin coating sponge, with the orifices of 

 the cloacffi scarcely elevated above the common surface 

 of the sponge, as represented by fig. 1, of the natural 

 size, in the present volume. In more sheltered situa- 

 tions it has still more or less of a coating form, but is 

 furnished with a series of irregular ridges or crests, on 

 which the excurrent orifices of the cloacse are situated, 

 as represented by fig. 2, Plate V, of the present 

 volume, of the natural size. In caves or other weU- 

 sheltered localities it assumes the form of congregated 

 lobular masses, as represented by fig. 362, vol. i, ' Mon. 

 Brit. Spongiadfe,' of the natural size, and by fig. 351 

 in the same plate, which represents a longitudinal 

 section of one of the mammas form, portions exhibiting 

 one of the cloacal cavities of the sponge and its internal 

 defensive spicula. X 50 linear. 



Figs. 3, 4, 5 represent the large, stout, equi- 

 angular, spiculated, triradiate, internal, defensive 

 spicula. X 80 linear. The basal radii of fig. 6 are pro- 

 jected backward in tripodal fashion. Very minute 

 specimens of this form are also found in the lining 

 membrane of the cloaca, one of which, X 660 linear, is 

 represented by fig. 89, plate iv, vol. i, ' Mon. Brit. 

 SpongiadEe.' 



Figs. 6, 7 represent two of the equiangular, triradiate, 

 skeleton spicula. X 80 hnear. 



Fig. 8. — One of the unicurvo-cruciform, tension 



