ORDER IV CRINOIDEA—FLEXIBILIA 163 
Order 4. FLEXIBILIA. Zittel. 
(Articulata, p.p. W. and Sp.,! non Miiller ; Ichthyocrinacea, Neumayr.) 
Base dicyclic, with stem or stemless ; the proximal ring of the base in the latter 
case enclosing a (2) dorsocentral (Carpenter). Arms branching, pinnulate or non- 
pinnulate. Tegmen, so far as has been observed, composed of orals and numerous 
exceedingly small, loosely united, movable pieces; orals asymmetrically arranged. 
Mouth and ambulacra exposed ; the latter roofed over by covering pieces and enclosed 
by side-plates. Ordovician to Carboniferous, and also Cretaceous. 
Family 1. Ichthyocrinidae. Wachsmuth and Springer. 
All plates of the calyx and of the arms from the radials upward united by loose 
suture or by muscular articulation. Base dicyclic ; infrabasals three, wnequal, small, 
rarely extending beyond the column, and fused with the top stem-joint ; basals five, 
small. Radials succeeded by one to six costals, which in species without interradials 
merease in size upwards, Brachials united by more or less waving sutures, and their 
lower edges furnished with tooth-like projections which fit into depressions on the 
subjacent plates , occasionally the projections are developed as separate patelloid plates. 
Interbrachials, when present, rather irregularly arranged. Tegmen squamous ; 
composed of five orals and numerous, very small, movable plates. Arms non- 
pinnulate, and exhibiting a very wide and shallow ventral groove. Column round ; 
the upper ossicles extremely short, and generally wider than the others. Ordovician 
to Coal Measures. 
Ichthyocrinus, Conrad (Fig. 270). IB very small; & and lower brachials 
laterally in contact at all sides; anals and interradials not represented. 
Crown appearing like a perfectly solid body when the arms are closed. 
Silurian to Coal Measures ; North America and Europe. 
Lecanocrinus, Hall (Fig. 271). Like the preceding, except that only four 
of the rays are laterally in contact, the two posterior ones being separated 
by a rhomboidal #4 and a somewhat larger JRA. Silurian; North America 
and Europe. 
Taxocrinus, Phill. (Figs. 272, 273). All five & separated by inter- 
brachials. Costals two, sometimes three. The posterior B larger than the 
others, truncated, and supporting an JRA. This is followed by a longi- 
tudinal row of small elongate supplementary anals, which are interposed 
between numerous very minute irregular pieces. Plates of the four regular 
interrays less numerous, larger, and more symmetrically arranged. Ordovician 
to summit of Sub-Carboniferous ; North America and Europe. 
Gnortmocrinus, W. and Sp. Like Tazocrinus, but with RA in addition to 
IRA; the former also supporting a longitudinal row of supplementary 
anals. Silurian; Gottland. 
Onychocrinus, Lyon and Cassed. Calyx depressed; arms spreading and 
talon-like. J& rarely projecting beyond the #, and closely or only partially 
1 [The three families embraced under this order, the Ichthyocrinidae, Marsupitidae, and 
Uintacrinidae, are included by Wachsmuth and Springer under the Articulata (Articulosa) as 
redefined by them. The non-pinnulate Jchthyocrinidae, however, are placed in a separate sub- 
order under the name of Articulata Impinnata ; while the Marsupitidae, Uintacrinidae, and most 
of the Mesozoic and Recent Crinoids constitute the second sub-order Articulata Pinnata.—TRAns. | 
