ECHINID^. 



251 



these animals are attached to submarine bodies by a longer or shorter 

 stalk, composed of calcareous rings similar to those of which the arms 

 are composed. 



The family Encrinidce, or Sea-lilies, fig. 109, includes an immense 

 number of fossil forms ; and one or two are still to be found in the 

 West Indian seas. These animals were all supported upon a long 

 stalk, at the extremity of which they floated in the waters of those 

 ancient seas, spreading their long arms in every direction in search of 

 the small animals which constituted their food. Each of these arms, 

 again, was feathered with a double series of similarly jointed append- 

 ages ; so that the number of separate calcareous pieces forming the 

 skeleton of one of these animals was most enormous. It has been cal- 

 culated that one species, the Pentacrinus Uriareus, 

 must have been composed of at least one hundred and 

 fifty thousand joints ; and " as each joint," according 

 to Dr. Carpenter, " was furnished with at least two 

 bundles of muscular fibre, one for its contraction, the 

 other for its extension, we have three thousand such 

 in the body of a single Pentacrinus an amount of 

 muscular apparatus far exceeding any that has been 

 elsewhere observed in the animal creation." 



A furrow runs along the inside of the arms ? 

 covered with a continuation of the skin of the disk ; 

 and from this the ambulacra are protruded, as in other 

 Echino-dermata. 



The third family, the Comatulidce, or Hair-stars, 

 includes a considerable number of animals, which 

 bear a great resemblance, both in form and structure? 

 to the Encrinidce. 



The Encrinus being supported upon a long flexible 

 stalk, formed of calcareous cylinders, is so close a re- 

 semblance, that when first discovered the young of Co- 

 matula was described as a Pentacrinus. These animals 

 are tolerably numerous in the seas of the present day, 

 and may be said to represent the living type of this 

 and the preceding class ; they are shown in fig. 116. 



In the family of Ophiuridce, so called from the resemblance of their 

 arms to serpents' tails (Gr. ophis, a snake, oura, a tail), the body forms a 

 roundish or somewhat pentagonal disk, furnished with five long simple 

 arms, which have no furrow for the protrusion of the ambulacra. The 

 Ophiuridce are exceedingly plentiful in all our seas, and their remains 



fig. 109. 



Encrinus, or 

 Sea-lily. 



