FOSSIL CRINOIDS. 137 



beginning with J. S. Miller, in 1821, who in not very clear terms made it the 

 basis of his general classification of the Crinoidea; and on account of it, at that 

 early day, placed his two genera, Poteriocrinus and Cyaihocrinus, in different 

 grand divisions, Semiarticulata and Inarticulata. With an equal lack of 

 accurate definition it was used by Johannes Mliller and von Zittel as the char- 

 acter of the Crinoidea Articulata It remained for P. H. Carpenter to state 

 the matter clearly when he said (Challenger Report. Stalked Crinoids, 145-6) 

 that "the name-giving difference between the Articulata and the Tessellata is 

 reduced to a supposed difference in the mode of union of the first radials with 

 the joints which they bear." 



Of this union there are at least four kinds known among the Crinoids: — 



1. Complete movable articulation upon wide, straight facets, filling the 

 distal face of the radials; with fossae, transverse ridge, paired muscles and 

 ligaments: The adolescent type above described, and which would probably 

 be found in the young of all the other types if we had specimens to examine. 

 Example in fossils, Eupachycrinus (PI. IV, fig. 17). 



PoTERiocRiNiDAE of Waclismuth and Springer (excepting Poterio- 

 crinus — an intermediate form). 

 Cupressocrinus. 



All Mesozoic and Recent Crinoids (with the exceptions noted 

 under 3). 

 Geological range. Ordovician to Present Time. 



2. Articulation with fossae, paired muscles and ligaments, but mostly 

 without complete transverse ridge; accompanying loose suture between other 

 plates, producing a flexible calyx admitting much mobility between apposed 

 faces of radials and brachials, whether incorporated by interbrachial plates or 

 not: A modification of No. 1, not very sharply defined. Example in fossils, 

 Forhesiocrinus. 



NoN-PiNNULATE Flexibilia, with morc or less continuous trans- 

 verse ridge in some cases, as in Lecanocrinus. 

 Geological range. Restricted to the Palaeozoic; Ordovician to Carbonif- 

 erous. 



3. Articulation upon undifferentiated joint faces, by concavo-convex sur- 

 faces, usually without transverse ridge, and with round facets less than width 

 of the radial: The senile condition above described. Example in fossils, Cya- 

 thocrinus (PI. IV, fig. 12). 



Cyathocrinidae of Wachsmuth and .Springer, with a few excej)- 

 tions. 



