ECHINODERMATA—CRINOIDEA. 543 



The most common species of the Upper Burlington of Missouri, 

 Illinois, Iowa, etc. 



141. D. whitei Wachsmuth and Springer. Mississippic. 

 Small (width less than three fourths of an inch), depressed- 

 globose, with slightly projecting arm regions. Surface of dorsal 

 cup ornamented with ridges and nodes, those of the tegmen each 

 with a sharp central tubercle. Arms 18, single. 



Keokuk of Indiana and Iowa ; Warsaw of Kentucky, Indiana 

 and Missouri. 



142. D. biturbinatus (Hall). Mississippic. 

 Resembles D. euconus, but calyx smaller and more globose, with 



height and width about equal. Arms 16, rarely 17, 

 Keokuk of Missouri and Iowa. 



143. D. montgomeryensis (Worthen). Mississippic. 

 Of medium size (about three fourths of an inch wide). Dorsal 



cup somewhat lower than the tegmen, with rounded sides. Arm 

 bases projecting tooth-like around the calyx. Arms 16, in pairs. 

 Plates of dorsal cup flat and smooth; plates of tegmen marked 

 with a small central tubercle. 



Keokuk of Indiana, Missouri and Iowa. 



144. D. originarius Wachsmuth and Springer. Mississippic. 

 Small (about one half an inch wide). Dorsal cup slightly higher 



than the tegmen, with straight sides. Arm bases projecting. 

 Plates convex, those of dorsal cup obscurely granular. Arms 16, 

 simple. 



Keokuk of Indiana and Missouri ; Warsaw of Missouri and 

 Illinois. 



145. D. euconus (Meek and Worthen). (Fig. 1872.) Mississippic. 

 Plates smooth. Arms 16. 



Keokuk of Indiana and Missouri ; Warsaw of Kentucky, Indiana 

 and Illinois. 



146. D. unionensis (Worthen). Mississippic. 

 Small (calyx three fourths of an inch wide). Dorsal cup some- 

 what shorter than ventral disk, which is very convex. Plates of 

 dorsal cup slightly convex, obscurely granular and ridged; those 

 of tegmen nodose. Arms 18, simple. 



Keokuk of Missouri ; Warsaw of Virginia, Alabama, Kentucky 

 and Missouri. 



