546 



NORTH AMERICAN INDEX FOSSILS. 



150. M. verneuilianus (Shumard). (Fig. 1875.) Mississippic. 

 Calyx smooth, sides scarcely concave. Arms usually 14. 



Very characteristic of the Upper 

 \^^j| Burlington of Illinois, Missouri and 



Iowa. 



LII. AoROCRiNUS Wachsmuth and 

 Springer. 



Small. Similar to Dorycrinus in 

 form of calyx, arrangement of plates 

 and of arms, i. e., arms in groups, 

 the anterior ray usually having the 

 fewest. Tegmen usually shorter than 

 dorsal cup, with smooth, nearly flat 

 plates except the posterior oral which 

 is convex or tubercle-like. Anal area 

 composed of small plates forming a 

 low ridge with anus near upper end. 



Differs from Dorycrinus in having 

 single arms and no spines. Devonic- 

 Mississippic. 

 151. A. parvus (Shumard). 



Mississippic. 



Calyx rotund, abruptly projecting 

 out at the arm bases and lobed. 



Upper Burlington of Missouri, Illi- 

 nois and Iowa. 



LIII. Reteocrinus Billings. 

 Calyx obconical. IB 5, sometimes 



Fig. 



1875. Mncrocrinus ver- 

 ueuilianus^ two specimens, one 



with arms, the other with proboscis barely protruding beyond the column, 

 and stem. (After Meek and B 5, large and protuberant. R and 

 °^^ ^"'^ fixed brachials forming broad, highly 



elevated ridges which pass insensibly into the arms. Between 

 these ridges are profoundly depressed interradial areas, composed 

 of minute irregular pieces. Arms 10 at their origin but usually 

 bifurcating. Tegmen depressed-convex, consisting of very small 

 pieces forming a continuation from the interbrachials. Anal open- 

 ing excentric, at top of a small protuberance. Column large, 

 pentagonal. Ordovicic. 



