OKPKR ii ( 'HIXOIDEA CAMERATA I 3!> 



Platycrinus, Miller (Figs. 229, 240). />' three, unsymmetnYal, fiv.jiiently 

 anchylosed. /,' long, large, laterally unitpd by close sutures, and furnished 

 siippi-inrly with a crescent- shaped articular facet. Succeeding the R, 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, ,ind consisting of three plates horizontally 

 arranged; they are in part interbrachial and in part 

 interambulacral. The higher interradials, when present, 

 strictly interainlmlaeral ; 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 



'O . , . . , I'lutHn-tHiisti-Hjiiitidin-tHl'i*, 



the upper and lower surfaces of the individual segments Austin sp. Carboniferous 

 1 icing slightly shifted upon one another. The stem is (reTtor^d'aiJe^de^oSrick"" 1 

 pierced 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. 



Eudadocrinus, 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 ; Eifel. 



Culicocrinus, Miiller. Transitional between Coccocrinus arid Platycrinus. 

 Calyx, as in the former, small and globose ; but the orals somewhat asym- 

 metrical. Arms bifurcated, heavy, biserial. Column round. Middle 

 Devonian ; Kifel. 



Cordylocrinus, Aug. 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. 



Miirsupiocrinus, Phill. Dorsal cup depressed, saucer-shaped. B and R as 

 in J'latycrimis. 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). 



