CLARS III 



CRINOIDEA 



223 



Calyx obconic to low cup-shaped. Arms branching two to four times, usually 

 more or less dichotomous, but in some species the inner arms of the dichotom 

 branch less frequently than the others, or remain simple, tending to the stage 

 of heterotomy seen in genera like Zeacrinus. Brachials cuneiform. Ventral 

 sac strong, usually enlarging distally. Stem 

 round or pentagonal, with cirri moderately devel- 

 oped. Carboniferous (Kinderhook to Upper Car- 

 boniferous) ; North America, Europe. 



This is a widely distributed form known in collections 

 generally as Scaphiocrinus, a name wliich lapses because 

 the type species belongs to the previously established 

 GrapJiiocrinus. It is one of the longest lived Paleozoic 

 genera, represented by a large number of species, and is 

 highly typical for this family. 



JFoodocrinus Koninck (1 Philocrinus Koninck) 

 (Fig. 324). Similar to preceding, but brachials 

 Short, quadrangular, arms usually heavier and 

 branching two to four times. Ventral sac stout 

 and apparently short. Stem short, tapering 

 distally, with scattered cirri. Lower Carbonifer- 

 ous; England. 



Zeacrinus Hall. Crown more or less ovoid, 

 often short, rounded above and below. Arms 

 heterotomous, usually closely abutting and infold- 

 ing ; the two outer branches of each ray the 

 stoutest, giving off at intervals successive pin- 

 nulate arms of nearly equal size and reaching to 

 the same height, always to the inside of the 

 dichotom, usually unbranched, but they may 

 divide. Brachials short, quadrangular. Ventral 

 sac short, usually diminishing upward. Stem 

 round, bearing long cirri distally. Carboniferous 

 (Kinderhook) to Coal Measures ; Mississippian 

 area. North America. 



Coeliocrinus White. Crown elongate, expand- 

 ing upward, with conical base. Arms as in 

 Zeacrinus, but not so closely abutting, and with 

 brachials cuneiform to interlocking. Ventral sac 

 inflated, balloon-shaped. Lower Carboniferous 

 (Burlington) ; Mississippian area. North America; 

 also Eussia. 



Hydreionocrinus Koninck. Crown short, flat 

 above, with concave base. Arms branching some- 

 what as in Zeacrinus, but very short, not rising 

 above the expanded rim of the sac ; brachials 

 interlocking to fully biserial. Ventral sac mushroom-shaped. Upper part of 

 Lower Carboniferous (Kaskaskia) to Coal Measures ; Belgium, Britain and 

 North America. 



Decadocrinus W. and Sp. Calyx depressed and base flat or concave. Arms 

 strictly isotomous, branching but once, giving two strong, pinnulate rami to 

 the ray, more or less angular or zig-zag. Brachials wedge-shaped, the longer 



Fio. 324. 



WocHlocrinvs macrodnc- 

 tylus (de Koninck). Per- 

 fect specinien from the 

 Lower CarlKiniferons of 

 Yorkshire (afl.-T <]>- Kon- 

 inck). 



