42 ECHINODERMA OF THE INDIAN MtTSETTM, PART VIT. 



7. CHANGES IN CLASSIFICATION. 



A few innovations in classification have been incorporated in this report which 

 seem to be called for by recent accessions to our knowledge. The family Tropio- 

 metridse, including the genera Tropiometra, Calometra, Ptilonietra, Pferometra, and 

 Asteromelra, has proved to be quite artificial. It is true that the species of all 

 these genera agree in having the muscles very greatly reduced and the arms end- 

 ing very abruptly as if broken off, but I find upon close' study that the muscles 

 have been reduced from three distinct original types, while the abbreviated arm 

 tips occur in one of the genera of the Thalassometridte. I have therefore retained 

 the famil}' Tropiometridse as covering Tropiometra only, a curious genus with no 

 very close affinities, created a new family Calometridse containing four new gen- 

 era for the numerous species which I formerly placed in Calometra, and placed 

 Ptilometra, Pterometra, and Asterometra in the Thalassometridae where they un- 

 doubtedly belong. The Charitometridoe I have made a family instead of a sub- 

 family, of equal rank with the family Thalassometridae (formerly the subfamily 

 Thalassometrinas). 



Recent discoveries have shown that the Zygometrida> are not nearly so 

 sharply differentiated from the so-called Hinierometridaj as was previously sup- 

 posed, and it has seemed best to discard the latter family altogetlier, raising the 

 three subfamilies previouslj' included within it to family rank. 



8. KEYS EOR THE IDENTIFICATION OF EAST 

 INDIAN CPJNOIDS. 



To facilitate the identification of Indian Ocean crinoids analytical keys are 

 given to the higher groups and to the genera. At the present time the determina- 

 tion of the families and genera presents a problem of no little difficult}^ owing to 

 the scattered literature and to the fragmentary way in which the present classi- 

 fication has been built up. This has been, unfortunately, unavoidable; it is due 

 mainly to the enormous additions to the numbers of known species within the past 

 few years, additions affecting first one group and then another, so that no stable 

 classification has heretofore been possible. Each classification proposed has in turn 

 fallen as a result of the discovery of many new species completely altering our 

 concept of the crinoid fauna as a whole. 



It has not been considered necessary to carry the keys Ijeyond the genera, as 

 almost al! of the species have been described within very recent years, and the 

 descriptions are easily obtainable. Moreover, large accessions to the numbers of 

 new species are to be expected in the near future which would soon render sj^eci- 

 fic keys obsolete and misleading, while it is not probable tliat the interrelation- 

 ships of the genera will be greatly altered for some time to come. 



The following keys are arranged only for the East Indian representatives of 

 the famiUes and genera given, and consequently are not always available for 



