ECHINODERMATA—CRINOIDEA. 



567 



199. F. agassizi Hall. Mississippic. 

 Larger than F. zuortheni, with interradial areas less depressed. 

 Burlington of Iowa. 



200. F. wortheni Hall. (Fig. 

 1906.) Mississippic. 



Interradial areas depressed. 

 Keokuk of Indiana, Illinois 

 and Iowa. ^V 



LXXVII. UlNTACRINUS 



Grinnell. 

 Symmetry perfectly in fives. 

 Plates thin. Stem wanting. B 

 5, enclosing a small, five-sided, 

 centrodorsal plate. Costals two, 

 the upper one axillary and sup- 

 porting two rows of distichals, which are succeeded by palmars. 

 Interbrachials numerous, the lowest ring interposed between the 

 costals. Arms ten, long and pinnulate, composed of very short, 

 almost circular, joints. Pinnules heavy and closely arranged, the 

 lower ones united by sutures and incorporated into the calyx. 

 Habitat free, floating as plankton. Cretacic. 



201. U. socialis Grinnell. (Fig. 1907.) Cretacic. 

 Calyx subglobose, composed of numerous, slightly convex plates 



joined together, with channelled sutures and without distinct sur- 

 face markings. IR, eight or nine in number, forming a rounded, 

 slightly elevated, shield-like area. IB often present. 

 Niobrara of Kansas and Utah. 



Fig. 1906. Forbesiocrinus worty- 

 eni, a complete calyx with arms, X 

 %. (After Meek and Worthen, 111. 

 Geol., V.) 



Order V. ARTICULATA Johannes Miiller. 

 LXXVIII. Pentacrinus Miller. 

 Calyx small, bowl-shaped, with dicyclic base. B and R united 

 by close suture ; R and lower brachials united by muscular articu- 

 lation or by a rigid suture. IB obsolete. Costals rarely more than 

 two, none of them pinnulate. Tegmen flexible, studded with small, 

 irregular plates. Arms very numerously divided. R laterally in 

 contact, but small, irregular plates frequently present between the 

 costals and distichals. Anal plates present only in the larval 



