170 RADIATA. 



Order 4. — Crinoidea. 



The Crinoids are among the most remarkable fossils that 

 lie entombed in the earth ; and it is only within the last cen- 

 tury and a half that their place in nature began to be under- 

 stood. For ages the superstitious or imaginative peasantry called them 

 "St. Cuthbert's beads," " rosary beads," " giants' tears," " fairy stones," 

 " wheel-stones," " screw-stones," and " pulley-stones." By early 

 naturalists they were termed " Trochites," " Entrochus," and " Encri- 

 nus." Their animal origin was established by Rosinus in 1719 ; and 

 their classification first correctly made by Miller in 1821. 



In a typical specimen, there are three parts : the root — a calcareous 

 secretion which fixes the animal to some sub-marine rock ; a hollow 

 jointed stem; and a corolla-shaped body provided with five solid arms, 

 independent of the visceral cavity and adapted to prehension. The 

 mouth is central and placed upwards ; the vent is situated on its 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 free, yet clinging to different bodies at the bottom of the ocean, as 

 the young Comatula ; and others still were disposed in such a way that 

 their bulbiform body was buried in the mud, as Marsupites. The geo- 

 graphical extent of the Crinoids is very limited ; and in their geological 

 range also they appear to be more restricted than other forms. Of the 

 105 genera described, 37 are confined to a single formation (Silurian) ; 

 and of 286 species, scarcely one extends beyond the rock or group of 

 which it is typical. None pass from the Paleeozoic to the Secondary. 

 They are among the earliest relics of animal organization ; and after 

 the microscopic organisms and Polyps, they have taken the largest share 

 in modifying the composition of the earth's crust. Like the Corals, 

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

 ocean, — whole strata of limestone being almost entirely made of their 

 remains. They appear first in the Lower Silurian (Potsdam), and cul- 

 minate in the Lower Carboniferous. There were over 500 Palasozoic 

 species ; 75 Jurassic ; 15 Cretaceous. The column is reared in nearly 

 all the Paloeozoic forms ; but pentagonal discs commence in the Lower 

 Silurian. Fixed Crinoids began with the Silurian period and decreased; 

 free Crinoids began in the Oolite and thence rapidly diminished. The 

 appearance of arms has been regarded as a stage of progress in de- 

 velopment : 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 



