Invertebrate Gallery of the Indian Museum, 103 



seen the orifice of the mouth : the inner concave surface 

 of the arms and of their branches is also covered with the 

 same thick skin, through which the ambulacra! feet emerge. 

 As in the Ophiuroidea, the viscera are confined to the 

 disk, and the ambulacral water-vascular system extends 

 along the arms and pinnules. 



2Kd. The chief characters of the Comatuiidae may be 

 learned from an examination of the fine specimens of 

 Actinometra in Case 27. In Actinometra the animal is 

 only fixed in its larval stages : in its adult stages it is free. 

 Here we find a conical disk, with a flat oval surface, from 

 which five long much-branched feathery arms radiate. 

 The under surface of the disk — whicfc is really the upper 

 or dorsal surface, for the animal moves about on its back, 

 face upwards — is covered with a pyramid of stout calcare- 

 ous plates, from which one or two whorls of stout segment- 

 ed "cirri" radiate. The cirri are prehensile, and by 

 means of them the animal anchors itself to foreign objects. 

 The upper surface of the disk — which is really the 

 under or ventral surface — is covered with a leathery skin 

 channelled by the wide ambulacral grooves as they pass 

 to the arms, and presents to view, near the margin, the 

 depressed oval mouth, and near the centre the long tubu- 

 lar anus. The arms are merely a repetition of those 

 of Metacrinus. In neither Metacrimis nor Actinometra 

 do we find a madreporic plate, this structure being absent 

 in the Crinoidea, in which Class the ambulacral system is 

 filled from the general body cavity or ccelom. 



The greater number of the Crinoidea are extinct, and 

 their fossil remains form vast beds of limestone rock, in 

 the Palaeozoic formations (Cambrian, Silurian, Devonian, 

 and Carboniferous) known as Crinoidal Limestone. 



The existing Crinoidea usually occur at some depth. 

 In the Indian area the Comatuiidae zre commonly dredged 

 on rocky bottoms at from 15 to 60 fathoms, and the Penta- 

 trinidx occur in the Andaman and Laccadive Seas at 

 and near 500 fathoms. 



This Class of the Echinodermata is represented in the 



