4 BRITISH SPONGIAD^. 



taken from small, very rare, of unique specimens, 

 while others subsequently obtained have been found to 

 be of much larger dimensions and to vary to a great 

 extent from the types of the species figured. The 

 structural and anatomical details are in truth the only 

 safe guides to the correct discrimination of species. 

 In a branch of natural history so comparatively new, 

 and which has been so imperfectly studied by our 

 predecessors, it naturally occurs that many of the 

 species have been determined from very imperfect 

 examples, and it therefore is highly desirable to obtain 

 as much additional information as possible with respect 

 to their variations in form, colour, and other characters, 

 and to register as many additional habitats as are 

 obtainable. 



" It is, moreover, strikingly apparent from the 

 many new species continually being found among the 

 Sponges dredged and otherwise collected by British 

 naturalists, that those already described do not by any 

 means comprise the whole of our British .rauna, and 

 it is highly probable that future labourers in this 

 interesting field of natural history will add very con- 

 siderably to their number." 



