PENTACRINUS ; ENCRINITES. 



461 



by the modification of some of these for particular purposes 

 a specialisation, or setting-apart, for some object of a more im- 

 portant nature, than those general functions to which they all 

 contribute. But the simple actions, which alone can be performed 

 by the arms of the Pentacrinus, are all that it needs for the 

 grasp of its food. 



1019. The general "structure of the Encrinus, of which no 

 recent species exists, bears a close affinity with that of the 

 Pentacrinus. The body and jointed stein exhibit rather a rounded 

 than a pentagonal form ; the latter is often des- 

 titute of secondary arms ; and the principal 

 branches do not ramify witli the same minute- 

 ness as those of many Pentacrini, but rather 

 resemble in their distribution those of the 

 Comatula. The stalk is attached by a sort of 

 spreading root, like that of many Corals ; and 

 we must therefore believe this tribe of Crinoi'dea 

 to havebeen entirely fixed. Besides the Encrinus 

 and Pentacrinus, there are many other extinct 

 genera of Crinoi'dea, which present a very 

 beautiful series of forms, all referable to the 

 same general type ; but on these our limits 

 forbid us to dwell. In the recent species of 

 Crinoi'dea, one or two of the arms may occa- 

 sionally be found, of much smaller size than the 

 rest, and apparently in process of replacing others which have 

 been accidentally lost. Among the fossil Crinoi'dea, such instances 

 are by no means rare. 



FIG. 607. ENCRINUS. 



ORDER III. FISTULIDA. 



1020. This Order may be regarded as connecting the 

 Echinida^ which may be considered as the types of the Class, 

 with the Articulated series. In some respects it may be con- 

 sidered to present a higher grade of organisation than we else- 

 where meet with among the Echinodermata ; but this does not 



