EMIiUYOLOOICAL CLASSIFICATION. CI 



it is only afterwards that they are developed (PI. \'il. Fitj. \ ; and PI. 

 VI. Fifjs. 10, 11, 12). In fact, the tentacles of our young Starfish, in its 

 earlier stages, resemble those of Astropecten, Luidia, and Ctenodi.sciis. 

 We are, therefore, at once provided Avith a set of characters taken from 

 the young, enabling us to decide the comparative value of the various 

 features, and the order in which they are to be taken. From the tenta- 

 cles alone we are fully justified, upon enibryological data, in placing 

 Starfishes with pointed tentacles lower than those which have disks, like 

 Asteracanthion. Another embryological feature is the fact that the em- 

 bryo lias only two rows of tentacles, -while in the adult Asteracanthion 

 Ave find the tentacles arranged in four rows. [The arrangement of the 

 ambulacral tentacles into furrows seems due simply to the crowding to- 

 gether of adjoining plates in consequence of increasing age, and has not 

 the systematic value formerly assigned to it.] Combining these charac- 

 ters, as we find them in the adults, we have at once good and conclu- 

 sive reasons for placing all those Starfishes which have, like Ctenodis- 

 cus, a pentagonal outline, and at the same time pointed tentacles, low- 

 est in the scale ; next in order would come the Starfishes with pointed 

 rays and pointed tentacles, without suckers, like Luidia and Astropecten ; 

 above them pentagonal Starfishes, with plates like Anthenea and Hippas- 

 teria, and two rows of tentacles, provided with suckers; then those with 

 more prominent rays, and tentacles also ending in suckers, like Penta- 

 ceros and Artocreas ; higher still, the Starfishes, with long slender arms, 

 and only two rows of tentacles with suckers, such as Cribrella, Opliidi- 

 aster, and the like ; while- highest in i\\Q order we should place the gen- 

 uine Asteracanthion, with four rows of tentacles, with suckers, and highly 

 developed spines on the abactinal area. 



The same principles applied to the different families would place Star- 

 fishes having plates without spines lower than those in which the net- 

 work of limestone is covered with spines on the abactinal surface. This 

 classification is not very different, as fiir as regards the order from that of 

 the three families proposed by Miiller and Troschel. It differs materially, 

 however, from the standing given to ])entagonal Starfishes in a short paper 

 by Professor Agassiz, in the Proceedings of the Natural History Society 

 of Boston. From this it is plain, that the mere study of the adult is not 

 a sound foundation for a natural classification. The echinoid characters 

 of the young Starfishes were not known at that time, which nnouKI natu- 



