5i8 



NORTH AMERICAN INDEX FOSSILS. 



60. P. americanus Owen and Shumard. Mississippic. 

 Dorsal cup more than once and a half as wide as high. Plates 



ornamented by coarse granules arranged concentrically around their 

 margins. Suture lines channeled through the beveling of the 

 plate edges. 



Burlington of Missouri, Illinois and Iowa. 



61. P. burlingtonensis Owen and Shumard. (Fig. 1839.) 



Mississippic. 

 Ventral disk depressed hemispherical, bearing an incurving anal 

 tube 5 or 6 mm. long. 



Burlington of Missouri, Illinois, Iowa and New Mexico. 



Fig. 1840. Platycrinus halli: a, calyx Fig. 1841. Platycrinus subspinosus. 

 with stem; c, d, outer and side views of (After Meek and Worthen, Pal. 111., II.) 

 part of arm. (After Meek and Worthen. ) • 



