CRINOIDEA. 143 



and "Eci'iims." Their animal origin was established bj Rosinus 

 in 1719 ; and their classification first correctly made by Miller in 

 1821. 



In a typical specimen there are three parts : the root — a cal- 

 careous secretion which fixes the animal to the sea-bottom ; a 

 lioUow jointed stem, and a corolla-shaped body provided with 

 five to ten solid arms, independent of the visceral cavity, and 

 adapted to prehension. The month is central and opens upwards ; 

 the vent is situated on the side. The normal position of the 

 Crinoid is the reverse of the Star-fish and Echinus. There were 

 three modes of existence: some were 'fixed in the midst of coral- 

 banks at great depths, as Encrinus liliiformis ^ others were fi-ee, 

 yet clinging to the bottom of the ocean, as the young Cornatula 

 {Antedon) ; and others still were disposed in such a way that 

 tlieir bulbiform body was buried in the mud, as Marsupites. 

 The geographical extent of the Crinoids is very limited, and in 

 their geological range also they appear to be more restricted than 

 other forms. No forms pass from the Palseoz'oic to the Secondary. 

 They are among the earliest relics of animal organization, and 

 after the Protozoa and Actinozoa they have taken the largest 

 share in accumulation of rock material. Like the corals, their 

 chief function seems to have been tlie secretion of lime from the 

 ocean, — whole strata of limestone being almost entirely made 

 of tlieir remains. They appear first in the Cambrian (Pots- 

 dam), and culminate in the Lower Carboniferous. The column 

 is round in nearly all the Palaeozoic forms, but pentagonal discs 

 commence in the Lower Silurian. Fixed Crinoids began with 

 the Silurian period and decreased; free Crinoids began in the 

 Oolite. The appearance of arms has been regarded as a stage 

 of progress in development ; from that moment, the variety of 

 forms augments with astonishing rapidity. The solid calyx of 

 Cystidea diminishes steadily, and in Pentacrinus barely forms a 

 basis for the internal parts. Finally, in the Upper Jurassic, it 

 frees itself from the pedicle, 'and in the form of Comattda 

 {Aiitedovb) enjoys the faculty of locomotion. The Comattda, 

 Pentacrinus Caput-medusce, and Rhizocrinus are the living 

 representatives of the class. The Cystids, as also the Blastoids 

 have been separated from the true crinoids (Brachiata) into dis- 

 tinct orders. 



