VI INTRODUCTION. 



cular species I have made a point of not choosing 

 exceptionally fine ones for figuring, but those repre- 

 senting about the average size and form, as best illus- 

 trating the general characters of the species. 



The carrying out of this design necessitated a com- 

 plete review of the structural peculiarities of the whole 

 of the British species, and theaccomplishment of this re- 

 examination of them has led to the discovery of several 

 errors of generic and specific determinations in Vol. II, 

 of this work, and to their rectification in the present 

 volume. Some of these errors have originated in the 

 dilapidated condition of the single type-specimen that 

 was the subject of examination and description, while 

 in other cases generic and specific alterations have 

 naturally arisen from an extended and more critical 

 acquaintance with the British Spongiada3. 



The following is a list of the alterations in the 

 genera and species that have been effected. 



Hymeniacidon lingua, ( Mon. Brit. Spongiadae,' Vol. 

 II, page 187, is now Rapldodesma lingua, Plate XXVII, 

 Vol. III. 



Hymeniacidon floreum, Vol. II, page 190, is now 

 Raphiodesma floreum, Plate XXXVII, Vol III. 



Hymeniacidon jecusculum, Vol II, page 198, is now 

 Microciona jecusculum, Plate LXXXIII, Vol. III. 



Hymeniacidon BucMandi, Vol. II, page 226, is now 

 Battersbyia Bucldandi, Plate XCII, Vol. III. 



Hymeniacidon plumosa, Vol. II, page 133, is now 

 Microciona plumosa. 



Microciona carnosa, Vol. II, page 133, is now Micro- 

 ciona plumosa. 



Holicliondria Hyndmani, Vol. II, page 264, is now 

 Isodictya Hyndmani, Plate XLVI, Vol. III. 



Chalina seriata, Vol. II, page 376, is now Oplilita- 

 spongia seriata, Plate LXV, Vol. III. 



Isodictya robusta, Vol. II, page 347, is no longer to 

 be considered a species, as it was founded on a fragment 

 of Desmacidon Jeffreysii before my ultimate acquaint- 

 ance with more perfect specimens of that species. 



