ORINOIDS. 



159 



Oa aceount of their great importance at the close of the 

 Paleozoic, it is, perhaps, advisable to call attention in this place 

 to certain anatomical structures which, in these organisms, are 

 of prime value in classification ; and especially since the nomen- 

 clature of the parts has undergone lately some radical changes, 

 more in harmony with the results of recent morphological 

 researches. The taxonomy is essentially that employed by 

 Carpenter and Wachsmuth & Springer. 



Forming as they do one of the great divisions of a sub- 

 kingdom, the stalked echinoderms present a striking contrast 

 to the classes most closely related. Instead of being able to 

 move from place to place, the " stone-lilies," during life, were 

 fixed to submerged objects by means of long, somewhat flex- 

 ible stems. Only in exceptional cases were they free-swimming, 

 as in the recent Antedon and Actinometra. Like other echi- 

 noderms, the skeletal parts of the feather-stars are made up of 

 a great number of calcareous ossicles or plates, more or less 

 symmetrical in outline, and definitely arranged and fitted in 

 accordance with a fundamental plan. In general structure the 



ancient forms 

 were very much 

 like those now 

 existing. But 

 there are at the 

 same time some 

 very marked dif- 

 ferences. 



A typical cam- 

 erate crinoid, as 

 for instance Ac- 

 tinocrinug(fig. 9), 

 illustrates very 

 well all the more 

 important fea- 

 tures. The chief 

 modifications of 



Plan of Actinocrinus . 





