Messrs. Austins' Arrangement of the Crinoidea. 107 



and that their inalienable natural rights may be preserved 

 intact. 



Our objections to Professor Forbes's arrangement chiefly 

 apply to the characters of his division s, which, however na- 

 tural they may be as regards the recent animals, are wanting 

 in reference to the calcareous framework of fossil species, by 

 which alone we can study their organization and arrive at 

 satisfactory conclusions respecting their probable manner of 

 growth, propagation, alimentation, in a word their habits, and 

 the structure and functions of their numerous organs. 



The aquiferous system, with its connexion with the organs 

 of progression, which Mr. Forbes makes the sole distinguish- 

 ing character of his orders, and which he has shown to be 

 wholly wanting in his sixth order Vermigrada (Sipunculidai), 

 would, if adopted, exclude our proposed first order Cionacineti 

 (fixed Crinoidea) from our class Pinnastella, as would the di- 

 stinguishing characteristics of his fourth order Cirrhi-Spini- 

 grada (Echinida) exclude our order Columnidce or fixed Echi- 

 nidte, which contains several genera and species of our class 

 Adelostella. 



In our proposed arrangement of the Echinodermata, we 

 have endeavoured to obviate the difficulties referred to, and 

 to establish our divisions on a combination of anatomical and 

 zoological evidence adduced from the comparison of recent 

 and fossil species. 



Synopsis of the proposed arrangement : — 



Subkingdom Centronix, Pallas. 

 Section Echinodermata. 



Body more or less protected by a shelly covering, com- 

 posed of variously shaped calcareous plates imbedded in the 

 substance, or attached to the surface of the skin. These 

 pieces are formed by the deposition of earthy particles round 

 certain central points, so that when fully developed they ob- 

 serve a well-defined arrangement which is easily traceable into 

 certain distinct forms, each peculiar to its kind. This external 

 covering, though formed of numerous pieces, continues firmly 

 united during the animal's life ; but after death, in consequence 

 of the liability of the investing membrane to destruction, the 

 bone-like plates become incoherent. By the mode of structure 

 pointed out, the increase of the animal as regards the size and 

 number of the plates is duly provided for, and injuries of the 

 shelly coat from external violence are readily repaired by the 

 renewed deposition of calcareous matter. 



All the known Echinodermes are marine, ami are sustained 

 by animal food. 



