ECHINOIDEA. II. I I 



nothurida and Echinometrida, or better still, to read the chapter <>n the classification of the Diadem- 

 atids in my paper <>n the Siam-Echinoidea (pp. 40 — 56) will recognize that my classification is not 

 based on the pedicellarise alone. It is true that my classification of the Cidaridce is almost exclusively 

 based upon the structure of the pedicellarise; but that is due to my inability to find other characters 

 which could be used with success. Any reader of my introductory remarks on the Family Cidaridce 

 will recognize that I have not omitted to take other characters into consideration, while the conclusion 

 of that chapter is as follows (p. 31): When in the diagnoses of genera given here other features than 

 pedicellarise and spicules have only been mentioned exceptionally the opinion of course is not that 

 these structures should be sufficient for definitive diagnoses. It has already been emphasized above, 

 and I shall here emphasize once more that all these structures must be thoroughly examined in order 

 to get the mutual relations of the forms established. That I have here only treated the pedicellarise 

 more thoroughly is a consequence of the fact that neither my material nor my time has permitted 

 me to treat the other features more particularly. The system of the Cidarids cannot get its definitive 

 formulation, until all features have been examined in a greater number of species (or best in all 

 species). What is given here is a provisional classification, which can scarcely be correct throughout... 



Whilst I must thus decidedly protest against the accusation of having based my classification on a 

 single character, I beg to suggest to Professor Agassiz whether that would not suit the classification 

 of the Eckinometridce and Echinidce given in the Revision of Echini . These Families are founded 

 exclusively on the number of pores in the ambulacral plates, all the genera with only three pairs of 

 pores being included in the family Echinidce, those with more than three pairs of pores in the family 

 Eckinometridce. And as for the impossible associations resulting from such artificial divisions according 

 to one character I might suggest to Professor Agassiz whether the placing of He imped inn. Phymo- 

 soma. Echinus, Toxopueitstcs, Tripneustes and Evechinus (Heliocidaris) in one subfamily, Triplechinidce, 

 as is done in the Revision , does not deserve to be thus characterized. 



Professor Agassiz speaks in a very depreciatory manner of the results of my classification, which 



culminate in such impossible associations that we are loath to follow his lead . It would have been 

 very interesting to hear some instances of these impossible associations, but unfortunately Professor 

 Agassiz confines his examples to a few Cidarids. It scarcely seems fair to condemn the whole of my 

 results on the evidence of a few debatable cases among the Cidaridce. the classification of which 

 family is expressly stated to be purely provisional. I should like to learn what are the impossible 

 associations in my classification of the Echinothuridce, Ecliiiwmetridce and the Echinida, the more so, 

 since it was the greater naturalness of the associations resulting from my classification which were 

 to my mind a proof of its correctness. I will, however, leave it to others to compare my arrangement 

 of the forms included in, let us say. the genus Strongylocentrotus or in the Family Echinometridce with 

 the arrangement given in the Revision of Echini . And upon the whole I venture to believe that, 

 since Professor Doderleiu has now accepted my classification of these groups in the main points, it 

 will be agreed, at least, that it cannot be so very unnatural; otherwise, so careful and judicious a natu- 

 ralist, with so profound a knowledge of the whole class, would certainly not have accepted it. 



Regarding the use of pedicellarise in the definition of systematical characters of Echini Professor 

 Agassiz agrees that it may be desirable to employ all the data possible from whatever source, 



2 



