500 



NORTH AMERICAN INDEX FOSSILS. 



small anal opening. Mouth beneath the tegmen. Stem composed 

 of thin joints. Devonic. 



Fig. i8io. Haplocrinus clio. Opposite views of two speci- 

 mens, X6. (After Hall.) 



4. H. clio Hall. (Fig. 1810.) Devonic. 



Very small, pentagonal in upper view, with 

 protruding arm bases. 



Marcellus of New York. 



IV. Symbathocrinus Phillips. 

 Calyx small, bowl-shaped. B 3, unequal. 

 R 5, nearly equal. Tegmen formed of five 

 small orals, the posterior the largest. Anal 

 tube long and slender. Arms 5, long, simple, 

 composed of thick plates with sharp edges. 

 Mississippic. 



5. S. dentatus Owen and Shumard. 



Mississippic. 



Slightly smaller than 5". robiistus and upper 

 part of calyx more contracted, tending to be- 

 come spindle-shaped. 



Burlington of Missouri and Iowa. 



6. S. robustus Shumard. (Fig. 181 1.) 



Mississippic. 

 Surface of calyx finely granulose. Margin 

 of basal excavation finely crenulate. 

 Keokuk of Kentucky and Illinois. 



Fig. 181 1. Symbatho- 

 crinus robustus^ X Yi- 

 (After Meek and 

 Worth en. ) 



Order II. FISTULATA Wachsmuth and Springer. 

 V. Hybocrinus Billings. 

 Calyx cup-shaped or obconical. B 5, high. The right posterior 

 R compound, the inferradial supporting the ventral sac, the super- 



