THE CRINOIDEA 171 



SUB-CLASS 2. DICYCLICA, Bather (1899). 



Crinoidea in which the base consists of BB and IBB, the latter being 

 liable to atrophy or fusion with the proximale, but the aboral prolonga- 

 tions of the chambered organ are always radial ; new columnals may or 

 may not be introduced at the proximal end of the stem. 



ORDER 1. Dicyclica Inadunata 



( = IXADUNATA, W. & Sp. pars, emend.). 



Dicyclica in which the dorsal cup primitively is confined to the patina 

 and occasional intercalated anals, and no other plates ever occur between 

 RR (Grade : Distincta) ; Br may be incorporated in the cup, with or 

 without iBr, but never rigidly, and their corresponding Amb remain 

 supra-tegminal (Grade : Articulata) ; new columnals are introduced at 

 the extreme proximal end of the stem. 



This order, so far as its Palaeozoic genera are concerned, corresponds 

 roughly to the Inadunata Fistulata of Wachsmuth & Springer, and 

 entirely to the Inadunata Dicyclica of Bather with an error or two 

 corrected ; but it includes also some of Muller's Articulata and some of 

 Wachsmuth & Springer's Larviformia. The latter authors have them- 

 selves proved the connection of the Encrinidae and Pentacrinidae with 

 their Fistulata. The distribution of the 70 genera into families would 

 present no great difficulty, were a purely morphological classification our 

 aim. One might use, as has been done, such characters as the presence 

 or absence of pinnules, of an anal tube, of a radianal, of articulation 

 between cup-plates, or of simply bifurcate as contrasted with dichotomous 

 arms. But there is every gradation in the development of these characters, 

 pinnulate forms being derived from non-pinnulate, the radianal gradually 

 disappearing, articulation of plates developed as need arose, and so on. 

 Hence the great division into Cyathocrinidae and Poteriocrinidae (W. & 

 Sp., 1886 ; Zittel, 1895) cannot meet the needs of the phylogenist. An 

 attempt to sketch the actual race-history (Bather, 1890) resulted in the 

 recognition of a distinction between Dendrocrinus and its allies, with their 

 broad radial facets and thin tegmen on the one hand, and Cyathocrinus 

 and its allies, with narrower facets and more solid tegmen on the other, 

 while the pinnulate forms were all derived from the Dendrocrinidae. 

 This distinction, subsequently strengthened (Bather, 1893), has been 

 made much of by Jaekel (1895), who divides all his Fistulata into 

 Cyathocrinacea, Dendrocrinacea, and Poteriocrinacea, the last group being 

 derived from the Dendrocrinacea, and giving rise to the Articulata 

 (Jaekel). It is therefore but a slight step to establish two sub-orders, 

 Dendrocrinoidea and Cyathocrinoidea. Of these the latter were the first 

 to be specialised and the first to disappear. The Dendrocrinoidea moved 

 more slowly and went further even to our own day undergoing modi- 

 fication in the development of the anal tube, in the pinnulation of the 

 arms, and in the relation of arms to cup. Moreover, from them branched 

 off the order Flexibilia, probably on more than one occasion. 



