NOTE TO PART IV. 



The lithographic stones of six plates, containing the anatomy of Strongy- 

 locentrotus Drobachiensis and of Echinarachnius parina, were destroyed, 

 together with the original drawings, and the bulk of my notes on the 

 subject, in the great conflagration of November 9, 1872. They were the 

 accumulation of several years of more or less consecutive work on living 

 specimens of the two more common species of the New England coast. 

 My observations on S. Drobachiensis and Echinarachnius parma were in- 

 tended as the basis of a critical revision of many of the doubtful points 

 of the anatomy of the order, and at the same time, taking these two 

 species as types of their allies, I hoped to give as complete a history as 

 possible of the structure of two of the suborders of the Echini. This, in 

 connection with the anatomy of Spatangus, lately published by Hoffman, 

 would have given us a tolerably full account of the whole order. 



This exposition I must now leave for future special monographs, and I 

 here add a revision of the Anatomy and Embryology of the order, based 

 upon what I have myself observed, taking in turn each of the three sub- 

 orders, in the discussion of the special points of structure. It will of course 

 be impossible for me, on account of the loss of so man}' of my plates of 

 reference, to make Part IV. as complete as it would otherwise have been, 

 and I am compelled to print a much less satisfactory exposition of this part 

 of the subject than I hoped to be able to publish. 



ALEXANDER AGASSIZ. 



Cambridge, January, 1874. 



