SECT. vi. ECHINODERMATA. 175 



to a substance at the bottom of the sea. During the 

 Jurassic period, miniature forests of these beautiful ani- 

 mals flourished on the surface of the Oolite strata, then 

 under the ocean. Myriads of their fossil remains are 

 entombed in the seas, and extensive strata of marble are 

 chiefly composed of them. Their hollow joints are known 

 in several parts of England as wheel stones, and as St. 

 Cuthbert's beads on the Northumbrian coast, in honour 

 of the patron saint of Holy Island, where they abound. 

 The Crinoidea are of two kinds : the Encrinites, which 

 chiefly flourished in the Palaeozoic period and are now 

 represented by a minute species (Khizocrinus Lofo- 

 tensis) lately discovered on the coast of Norway by 

 Professor Sars, have a smooth, cylindrical, jointed stem ; 

 and the Pentacrinites, which began at the Lias, and have 

 a five-sided jointed stem, the present representative of 

 which is the Pentacrinus caput-Medusse, found in the 

 West Indian seas. 



The hollow, five-sided, calcareous, jointed stem of the 

 living Pentacrinite is filled with a spongy substance, and 

 supports a cup on its summit, containing the digestive 

 organs, mouth, and tentacles of the animal. The cup 

 is formed of a series of calcareous plates, and from its 

 margin five long many-jointed rays diverge, each of 

 which is divided into two-jointed branches. Groups of 

 curled filaments, called cirri, are placed at regular dis- 

 tances from the bottom of the stem to the extremity of 

 the rays, while, on the opposite side of the rays, there 

 are groups of feathery objects called pinnse at each joint. 

 Food is caught by the tentacles and digested by the 

 stomach and viscera at the bottom of the cup, from 

 whence vessels diverge through a system of canals in 

 the axes of the rays, pinnse, and down the stem, all of 

 which convey sea-water mixed with nutritious liquid, 

 for the nourishment of the animal. 



The genus Comatula are star-fishes, believed to have 



