ORDER II CRINOIDEA—CAMERATA 139 
Platycrinus, Miller (Figs. 229, 240). B three, unsymmetrical, frequently 
anchylosed. & long, large, laterally united by close sutures, and furnished 
superiorly with a crescent-shaped articular facet. Succeeding the £, and 
united with them by close sutures, is a row of small axillaries. These are 
often so minute as to be completely hidden within the 
radial facets, as is also the case sometimes with the first 
distichals. First row of interradials on a level with the 
arm-bases, and consisting of three plates horizontally 
arranged ; they are in part interbrachial and in part 
interambulacral. The higher interradials, when present, 
strictly interambulacral ; plates of the anal interray more 
numerous than those of the four regular sides.  Orals 
large, asymmetrical, and resting against the interradials. 
Covering pieces of the ambulacra generally exposed, very 
rigid, and incorporated into the tegmen. Anus either 
eccentric, or placed at the end of a short thick tube. 
Arms uniserial at their lower ends, but gradually becom- 
ing biserial. Column elliptical and twisted ; the axes of , . <trigintidactylus 
the upper and lower surfaces of the individual segments Austin sp. ‘Carboniferous 
being slightly shifted upon one another. The stem is eet cee Cee, 
piereed by a very minute axial canal, and gives off cirri 
toward the distal end. Extremely scarce in Devonian, but abundant in Carbon- 
iferous. P. laevis, Mill. ; P. hemisphaericus, M. and W. 
Eucladocrinus, Meek. Calyx and stem as in Platycrinus, but having the 
rays produced laterally into large tubular appendages, from which biserial, 
pinnule-bearing arms are given off alternately throughout their entire length. 
Sub-Carboniferous (Burlington and Keokuk Groups). 
Coccocrinus, Miiller (Fig. 227). Like Platycrinus, but the costals wider, 
and forming together with the interradials a part of the dorsal cup. Costals 
two, succeeded by two distichals, of which the upper one is axillary ; inter- 
radials only one to each side. Orals large, triangular, abutting against the 
interradials, and forming nearly the whole of the ventral surface. They are 
separated from one another by a deep angular groove, closed at the bottom. 
Anal opening in the suture between the posterior interradial and its corre- 
sponding oral. Silurian; Tennessee. Devonian ; Kifel. 
Culicocrinus, Miiller. Transitional between Coccocrinus and Platycrinus. 
Calyx, as in the former, small and globose; but the orals somewhat asym- 
metrical. Arms bifurcated, heavy, biserial. Column round. Middle 
Devonian ; Eifel. 
Cordylocrinus, Ang. Arrangement of calyx plates as in Platycrinus, but 
the tegmen higher, and arms uniserial. Column round, and bearing long 
cirri; the upper ones reaching nearly to the tips of the arms. Silurian ; 
Gottland. 
Marsupiocrinus, Phill. Dorsal cup depressed, saucer-shaped. 6 and £ as 
in Platycrinus. Radials rapidly spreading, and followed by a very small 
trigonal axillary ; this, together with the two superjacent distichals, is buried 
within the radial facet, so that the three plates are wholly or almost wholly 
supported by the radials. 'Tegmen composed of numerous small pieces ; anal 
opening eccentric. Column round, and traversed by a large axial canal. 
Silurian ; Gottland, England, and North America (Niagara Group). 

Fic. 240. 
