iv PREFACE. 



French, ten to the Leyden, seven to the Vienna, four to 

 the British, and two to the Berlin Museums. 



"Although I have described five or six times as many 

 species as any of my predecessors, I am certain that here- 

 after we shall find a great number of new species, as the 

 species of the West Coasts of Africa and America, and the 

 shores of Australia and the Pacific Ocean are almost un- 

 known to us, and there are evidently many gaps in the 

 families and genera. Indeed our best works on Natural 

 History must always be regarded as imperfect. 



"You desired that I should give a list and short cha- 

 racters of the few species mentioned by preceding writers 

 which I have not been able to identify with those that have 

 come under my observation ; but I have not considered this 

 desirable, as the descriptions are too short, or wanting in 

 precision, to be of any useful purpose, containing generally 

 little more than the generic characters, instead of being 

 comparative and distinctive of the species." 



Sir John Richardson, M.D., F.R.S. &c, has most kindly 

 compared Dr. Kaup's translation of the text with the ori- 

 ginal German version, to prevent any inaccuracies that might 

 have occurred from Dr. Kaup's want of knowledge of the 

 peculiarities of the English language. 



JOHN EDWARD GRAY. 



May 1, 1856. 



