172 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



they show great individual variability. The evidence offered by A. 

 Agassiz and Clark (: 07) cannot be ignored or denied, and we are there- 

 fore forced to conclude that neither spines nor pedicellariae can be de- 

 pended on to furnish unvarying characters. On the other hand, Duncan 

 errs in placing his reliance almost exclusively on the test and in neglect- 

 ing the characters afforded by the spines and pedicellariae. The classi- 

 fication used by A. Agassiz and the first one proposed by Doderlein 

 ('87) show a judicious balancing of the various characters, and un- 

 doubtedly must serve as the basis for the natural classification we are 

 seeking. Doderlein's latest arrangement of the Cidaridae does not ap- 

 peal to me as being well-balanced, for many excellent characters afforded 

 by the test and spines are neglected or given little weight, while the in- 

 teresting diversities of the pedicellariae are permitted to outweigh all 

 else. It seems to me there can be little question, either on a priori 

 grounds or as a result of observation, that the characters afforded by the 

 test are the most important in determining relationships among the 

 Cidaridae, and that those of the corona appear to be more reliable than 

 those of the abactinal system and actinostome. The size of the two 

 latter as compared with each other and with the size of the test are 

 useful factors in many cases, but there is considerable individual di- 

 versity in these proportions. This is true also of the arrangement of 

 the plates of the abactinal system, the position, form, and size of which 

 nevertheless often furnish characters of very great weight. The pri- 

 mary spines reveal obvious and tempting features, but these must be used 

 with caution, they are generally so variable. Curiously enough, how- 

 ever, in certain cases a character afforded by the primaries is very constant, 

 even though in nearly related species the same character may be very 

 variable. The pedicellariae well repay careful examination and often re- 

 veal interesting and constant peculiarities, but, as has already been em- 

 phasized, they, like the spines, are subject to great individual diversity. 

 Indeed, it seems to be true that a species which has very variable spines 

 is likely to have equally variable pedicellariae. The secondary, and even 

 the miliary, spines sometimes show characters of real value, although in 

 certain cases they are as variable as the primaries. The calcareous par- 

 ticles in the tube-feet seem to be so uniform in the family but so variable, 

 within these limits, in the individual that they afford no real help in 

 classification. 



In the classification set forth in the following pages I have attempted 

 to place the proper value on each of the features of Cidaridean anatomy 

 mentioned above, and I have also taken into account geographical and 



