8 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



the echinoderms the case is much more complicated than in the insects and crusta- 

 ceans on account of the difference in symmetry between the young and the adults. 



Sir Wyville Thomson long ago recognized this fact, that in tracing out the life 

 history of the echinoderms we are apparently dealing with two distinct organisms, 

 each apparently presenting all the essentials of a perfect animal, as had W. B. 

 Carpenter before him, but succeeding authors have shown a tendency to disregard 

 their warnings. 



On account of the curiously aberrant and sudden differentiation of the echino- 

 derms as a whole, and similarly of each of the constituent classes of the group, we 

 can never hope to ascertain the true interrelationships either of the echinoderms and 

 other annuals, or of the several constituent classes of the echinoderms, by any direct 

 method of comparison. 



The ancestral characters have become so modified by the adoption of radial 

 symmetry, and the bilateral young have become so specialized, that any direct com- 

 parison which is at all conclusive has now become impossible. 



We must therefore approach the problem by an indirect method, by the adop- 

 tion of hypotheses which will logically explain all the facts presented and win cover 

 all the data which we are able to accumulate, but which are not primarily the direct 

 and indisputable resultants attained by the correlation of these facts and data. 



SYNONYMY. 



The synonymy of the recent crinoids was in a decidedly tangled condition, 

 having been only partially elucidated by Carpenter, as he did not discuss in detail 

 any but the species collected by the Challenger. I therefore found it necessary to 

 enter into this phase of the subject somewhat deeply, especially in view of the fact 

 that the group contained a disproportionately large number of floating names 

 nomina nuda and unidentifiable supposed species which it was very desirable to 

 allocate if possible. I have attempted to bring together all the references to each 

 species that I could find, in the hope that future workers will be spared the formid- 

 able task of having again to review the enormous mass of literature. The synony- 

 mies given are, I believe, reasonably complete, though numerous notices of species 

 not here included will doubtless come to light in the future. The citations have, 

 with very few exceptions, been personally verified, and may be taken as representing 

 the works consulted in the preparation of this monograph. 



SYSTEMATIC TREATMENT. 



In the case of the comatulids it has been found necessary to multiply by about 

 a dozen times the number of genera previously allowed, and to create numerous 

 new families and higher groups. This was the unavoidable result of the discovery 

 of a vast number of new species, throwing a radically different light upon the inter- 

 relationships of the various forms. 



The different species of comatulids vary very greatly in the number and obvious- 

 ness of the characters by which they are separable from closely related species; two 

 species, perfectly distinct, may be separable only by a small minority of what are 



