472 



ENCRINITES. HOLOTHURIDA. 



Pentacrinus. The body and jointed stem exhibit rather a rounded 



than a pentagonal form ; the latter is often destitute of second- 



ary arms ; and the principal branches do not 



ramify with the same minuteness 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 Crinoidea to have been en- 



tirely fixed. Besides the Encrinus and Pen- 



tacrinus, there are many other extinct genera 



of Crinoidea, 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 Crinoidea, one or 



two of the arms may occasionally be found, of 



much smaller size than the rest, and apparently 



in process of replacing others which have been 



accidentally lost. Among the fossil Crinoidea, such instances 



are by no means rare. 



7og _ ENCRINT78 



ORDER IV. HOLOTHURIDA. 



1112. This Order may be regarded as leading from the 

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

 towards 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 

 entitle it to rank as the typical order of the class ; since its more 

 elevated character is only obtained by its approach towards a 

 very different type of organisation. This Order, which consists 

 of the Holothuria and its allies, is known by the comparatively 

 small amount of calcareous matter contained in the skin ; this 

 never forms an armour of plates and spines, but is met with only 

 in the shape of scattered grains. The skin is soft, and very 



