10 IXTRODUCTIOX. 



lay great stress upon priority in ti)e case of the nomenclature of orders or 

 families merely introduces endless confusion, and we are compelled either 

 to adopt the principle of limiting the names of well known subdivisions 

 in a manner which in no way conforms to the ideas of the original classi- 

 fier, or to introduce new names to be changed each time that the limits 

 of these subdivisions are expanded or contracted. Nothing seems to be 

 gained by the use of Scytodermata in place of Holothurians. The Asterida 

 of older authors included the Ophiurans, but to-day the Asterida and Ophi- 

 lu'ida are considered as equivalent groups. Yet we might gain precision 

 by adopting a new name to include both these orders, in order to contrast 

 them with the Echinida. We might adopt the name of Actinozoa, or any 

 other, to contrast the Echinids and Starfishes and Brittlestars with the 

 Crinoids on the one hand, and the Holothurians on the other ; or again, 

 we might adopt some name to include all the orders of Echinoderms except 

 the Crinoids, and contrast them with the Crinoids; — either of which would 

 repi'esent special points of view seeming to tend toward a subdivision of 

 Echinoderms into groups represented by the genera of the older writers, — 

 Caryocrinus, Pentremites, Pentacrinus, Ophiura, Asterias, Echinus, Holo- 

 thuria. These old generic names, or the groups they represent, thus 

 gradually passing into family, ordinal, or even class names of the Branch 

 of Echinoderms. 



It is interesting to note how frequently recent investigators are coming 

 back to antiquated classifications under different appellations. As we dwell 

 upon the affinities, or contrast them, in the several groups of the animal 

 kingdom, we find in the specialist a tendency to separate the group he 

 is investigating from those closely allied, while the general morphologist 

 is inclined to unite theui. 



The Echinodermata of Klein, as he originally defined them, would be 

 limited to Sea-urchins. The original limitation of Crinoids as defined by 

 Miller would clearly limit them to the Brachiate Crinoids. Subsequent 

 writers have expanded the limits of Crinoids with increasing acquaintance 

 of the fossil forms, and united to them the Cystids and the Blastoids. With 

 our greater knowledge of the last named groups, such an intimate associa- 

 tion does not seem fully justified, and we are now not seeking affinities, 

 but laying great stress on differences. No one would suggest the limita- 

 tion of Echinodermata to the Urchins, and we may ask the same indulgence 

 for the name of Crinoids, retaining that appellation for the group as a 



