ECHINODERMATA—CRINOIDEA. 517 



of the four regular sides. Orals large, unsymmetrical and resting 

 against the interradials. Covering pieces of the ambulacra usually 

 exposed, very rigid, and incorporated into the tegmen. Anus ex- 

 centric, either opening directly through the disk or placed at the 



Fig. 1838. Marsipocrinus prcematurus, Fig. 1839. Fiatycrinus burlingtonensis, 

 side and bottom view. (Ohio Pal.) calyx and two enlarged views of arms, X 



3. (After Meek and Worthen.) 



end of a short, thick tube. Arms uniserial at their lower ends, but 

 gradually becoming biserial. Stem elliptical and twisted, the axes 

 of the upper and lower surfaces of the individual joints being 

 slightly shifted upon one another. Axial canal minute. Devonic- 

 Mississippic. 



A. Dorsal cup deep, bowl-shaped, with much of the B visible in side view I- 



I. Interbasal sutures not prominent i. 



I. Plates smooth a. 



a. Arms six to a ray 61. P, burlingtonensis. 



a. Arms seven or eight to a ray 62. P. halli. 



1. Plates covered with nodes 66. P. hemisphericus. 



I. Interbasal sutures raised into ridges 2. 



2. Lower brachials with wavy sutures 67. P. huntsvillce. 



2. Lower brachials with the usual sutures b. 



b. Calyx small, with short compact arms 65. P. bonoensis. 



b. Calyx larger, with tapering arms 68. P, sarce. 



B. Dorsal cup shallow, bowl-shaped, with rarely more than the edges of the B visible 

 in side view 60. P. americanus. 



C. Dorsal cup discoid II. 



II. Plates deeply corrugated 63. P. discoideus. 



IL Plates nearly or quite smooth 64. P. subspinosus. 



