32 PALEONTOLOGY. 



Order 1. — Crinoidea. 



Char. — Body with ramified rays, supported temporarily or 

 permanently on a jointed calcareous stem ; alimentary 

 canal, with mouth and vent, both, as in Bryozoa, 

 approximated. 



The 1 stone-lilies," or crinoid star-fishes, formed a nume- 

 rous and important group in the palaeozoic seas, where they 

 obtained their maximum number and variety. M. d'Orbigny 

 describes thirty-one palaeozoic genera, two triassic, ten oolitic, 

 alid four cretaceous — of which latter three (Pentacrinus, Bour- 

 gueticrinus and Comatula) are found in the tertiaries and mo- 

 dern seas. The Crinoidea differ from the other echinoderms 

 in having the generative organs combined with the arms, and 

 opening into special orifices near their base. Nearly all the 

 genera, except Comatula and Marsupites (fig. 6, 9), appear to 

 have been attached either by the expanded base of the column, 

 as in Apiocrinits, or by jointed processes, as in Bourgueticrinus. 

 In many instances the lower part of the column throws out 

 innumerable root-like side-arms, which strengthen and support 

 it. The column is comparatively short in Apiocrinus Parkin- 

 soni, and extremely elongated in Pentacrinus Hiemeri. It is 

 round in nearly all the palaeozoic Crinoids ; and when five- 

 sided, the articular surfaces of the joints are simply radiated, 

 as in the rest. These joints are perforated in the centre, and, 

 when detached, are the " St. Cuthbert's beads" of story (fig. 

 6, 5).* In Platycrinus the stem is compressed, and the arti- 

 cular surfaces are elliptical. In the genus Pentacrinus, which 

 commences in the lias, the sculpturing of the articulations is 

 more complex (fig. 6, 8), but it is quite simple in the other 



* Casts, in chert, of the canal which passes down the crinoidal column are 

 called " screw stones:" and those limestones which abound in columns and 

 detatched joints are called " entrochal marbles." 



