l6o AN INTRODUCTION TO THE STUDY OF FOSSILS 



Fossil remains of these animals consist mainly of detached 

 portions of stems or scattered calyx plates. Complete forms, 

 preserving calyx, stem, and root, are 

 rare. 



Derivation of name. — Greek crinon, 

 lily, + eidos (old), form. The stalked 

 forms resemble lilies, as is noted also in 

 the common name of the class, " sea- 

 lilies." 



Pentacrinus (Fig. 62). 



Triassic to present. 



This form, unlike the starfish, has the 

 mouth, or ventral side, uppermost, while 

 the opposite, or dorsal, side is fixed to the 

 ground by a long flexible stalk. 



The animal is composed of a globular 

 body {calyx), from the upper surface of 

 which branched arms, and from the 



Fig 62.-Above stem joints j^^^.^j. ^^^i^^^ Jg gi,,en off the Stalk, 

 of the cnnoid, Pentacrinus _ ^ ^ 



asteriscus M. & H., from Embedded within the skin of all parts 



To ihrTefrthe^'iurface ^^^ ^^""^ calcareous platcs forming a 

 view of a joint (natural Strong protective skeleton. The stalk is 

 size); to the right five ^^^^ ^^ groovcd disks, resting One 



jomts, side view. Eelow, a . . . 



modern crinoid, Pentacri- upon the Other like a pile of coins, and 

 nus caput-meduscB (much piej-^ed at the Center bv a canal contain- 



reduced), from the Gulf ^ 



of Mexico. This shows ing a prolongation of the nervous and 

 the arms (concealing the blood vascular svstcms. Small branches, 



calyx) and the upper por- _ - _ ' 



tion of the stem. The the cirri, whose function is doubtful, are 



last is reproduced from -^ ^^ ^^^^ ^j^^ ^^^^ ^^^ ha\-e an in- 

 Lucas Animals before ^ 



man in North America." ternal and external structure similar to 

 that of the stem. In some cases, prob- 

 ably, the stalk was attached to the 

 ground by a branching root; more generally it was free, being 

 merely anchored to seaweeds, etc., by the entwining of the cirri 



Copyright, 1902, by D. 

 Appleton and Co. 



