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 Spongiada?. 



The following is a list of the alterations in the 

 genera and species that have been effected. 



Hymeniacidon lingua, ' Mon. Brit. Spongiad;i3,' Vol. 

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

 Vol. III. 



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

 Baphiodesma floreum, Plate XXXVII, Vol III. 



Hymeniacidon jecusculum. Vol II, page 198, is now 

 Microciona jecuscidum, Plate LXXXIII, Vol. III. 



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

 Battersbyia Bucklaudi, Plate XCII, Vol. III. 



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

 Microciona plumosa. 



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

 ciona plumosa. 



Halicliondria Hyndmani, Vol. II, page 2G4, is now 

 Isodictya Hyndmani, Plate XL VI, Vol. III. 



Gha.lina seriata. Vol. II, page 376, is now Ophlifa- 

 spongia seriata, Plate LXV, Vol. III. 



Isodictya robusta, Vol. II, page 347, is no lono-er to 

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

 of Desmucidon Jeffreysii before my ultimate acquaint- 

 ance with more perfect specimens 'of that species. 



