ECHINODERMATA—CRINOIDEA. 529 



96. S. sculptus (Hall). (Fig. 1856.) Mississippic. 

 Brachial trunks only five instead of the usual ten. 



Lower Burlington of Missouri, Iowa and New Mexico. 



97. S. concinnus (Shumard). Mississippic. 

 Usually larger than 5. sculptus, 5-angled, with almost flat ven- 

 tral disk. Surface mostly smooth, with low ridges only at margins 

 of plates. Rays five, each with two trunks. 



Upper Burlington of Missouri, Illinois and Iowa. 



98. S. pentagonus (Hall). Mississippic. 

 Of medium size (smaller than 5*. sculptus), and distinctly pent- 

 angular from upper and lower views. Dorsal cup nearly twice 

 the height of the tegmen. Calyx extensions 5, each bifurcating 

 Irom the second costals into two free trunks bearing the arms 

 from the sides. Plates but little convex, marked by radiating 

 ridges which form nodes in the center of the plates. Anal tube 

 strongly nodose. 



Lower Burlington of Missouri, Iowa and New Mexico. 



XXXVIII. Physetocrinus Meek and Worthen. 



Arrangement of plates up to the distichals as in Actinocrinus, 

 but anus opening through the tegmen and not at the end of a 

 tube. Arm bases projecting in a rim. Rays in two main divisions 

 which give off the arms. Orders of brachials from the costals up 

 consisting of a single plate which supports an arm at one side 

 and a higher brachial at the other. Ventral disk depressed at 

 top and plicated around the margin, its depressions alternating 

 with the brachial lobes. Mississippic. 



99. P. ornatus (Hall). Mississippic. 

 Of medium size (calyx usually not much exceeding one inch in 



width). Ventral disk nearly flat. 



Lower Burlington of Missouri and Iowa. 



100. P. ventricosus (Hall). Mississippic. 

 Large (calyx often one and one half inches or more wide). 



Ventral disk hemispherical. (Type of genus.) 

 Burlington of Missouri and Iowa. 

 34 



