ECHINODERMA TA—CRINOIDEA . 533 



high nodes. Tegmen as high as dorsal cup, pentagonal in outline. 

 Spines six. 



Keokuk of Kentucky, Indiana, Illinois, Missouri and Iowa. 



:o8. D. mississippiensis Roemer. Mississippic. 



Resembling D. gouldi in size and outline with pentagonal summit 

 and six spines which are somewhat shorter and more tapering. 

 Calyx deeply impressed and flattened posteriorly. Plates nearly 

 fiat to strongly nodose. 



Keokuk of Kentucky, Tennessee, Missouri, Illinois and Iowa. 



XLII. Agaricocrinus (Troost). 

 Calyx depressed globose. Dorsal cup greatly depressed, usually 

 with only the arm facets and portions of the interbrachials visible 

 in side view. B 3, small, arranged in a horizontal hexagon. R 

 small, supporting two primary brachials (costals), which are fol- 

 lowed by short distichals and, in rays with more than two arms, 

 by still shorter palmars. Interradials of the dorsal cup rarely 

 more than four, those of the tegmen numerous, especially at the 

 anal side. Arms two to four to the ray, long and ponderous, their 

 bases separated by narrow and long interbrachials. Tegmen high, 

 pyramidal the upper end occupied by a massive, button-shaped 

 central piece which is surrounded by four similar, but slightly 

 smaller plates, these constituting the orals. Anus in a posterior, 

 more or less protuberant area. Column long, composed of larger 

 and smaller pieces. Mississippic. 



A. Large (greatest width usually over I inch)., T. 



I. Dorsal cup scarcely visible in side view, i. e., calyx resting nearly or quite on 



the arm bases i. 



I. Calyx width nearly twice the height Il6. A. crassus. 



1. Width of calyx only slightly exceeding height a. 



a. Arms 16 117. A. nodulosus. 



a. Arms 12 (rarely I4) ii. 



II. Plates of dorsal cup convex 114. A. tuberosus. 



II. Plates of dorsal cup only slightly convex 113. A. americanus. 



I. Dorsal cup high though lower than tegmen 115. A. coreyi. 



B. Of medium size or small (greatest width usually one inch or less) II. 



II. Dorsal cup high, about the height of the tegmen 109. A. brevis. 



II. Dorsal cup low, scarcely visible in side view 2. 



2. Plates of ventral disk nearlyallflat b. 



b. Anal ridge present 118. A. splendens. 



b. Anal ridge absent no. A. planoconvexus. 



