174 CRINOIDS. 



Dorycrinus mississippiensis Roemer. 



Dorycrinus mississippiensis Roemer, 1853: Archiv. fur. Naturgesch., 



Jahr. xix, Bund I, p. 207, tab. x, figs. 1-3. 

 Adinocrinus mississippiensis^ var. spiniger Hall, 1860: Geol. Iowa, vol. I, 



sup., p. 54. 

 Dorycrinus mississippiensis Meek & Worthen, 1873: Geol. Sur. Illinois, 



vol. V, p. 380. 

 Dorycrinus mississippiensis Worthen, 1891 : Geol. Sur. Illinois, vol. VIII, 



p. 100, pi. xii, fig. 4. 



Calyx like that of D. gouldi, but with smoother plates in 

 the dorsal cup, and with longer spines. 



Horizon and localities. — Lower Carboniferous, Keokuk 

 limestone: Kahoka (Clark county); Keokuk (Iowa); War- 

 saw (Illinois). 



Gennaeocrinus trijugis Miller. 



Plate xxiii, flgs. 3a-b. 

 Blairocrinv^ trijugis M.\\\qt , 1891: Geol. Sur. Indiana, 17tli Ann. Rep., 

 adv. sheets, p. 69, pi. xi., figs. 1-3. 



Calyx of medium size, subglobose, slightly wider than 

 high, distinctly lobed around the periphery. Dorsal cup basin- 

 shape, flattened below, prominently ridged toward the arms. 

 Ventral side about as high as the dorsal, composed of rather 

 large plates, those toward the periphery bearing short, stout 

 spines ; anal opening eccentric, at the top of a short, ventral 

 tube. Basals three, equal, quite short. Eadials rather large; 

 costals small. Interradials numerous, continuous with those 

 of the ventral side. Anal interradius somewhat wider than 

 the others; the first plate similar to, and in the same circlet as, 

 the radials ; two plates in the second range, as in Actinocrinus, 

 and smaller ossicles above. Stem circular, of medium size. 

 Sculpturing of the dorsal cup consists of rather sharp ridges 

 running from the center of each plate to the centers of the 

 adjoining pieces, and thus cutting up the surface into numerous 

 small triangular areas ; the radial ridges are somewhat more 

 pronounced than the others, and increase in size until they pass 

 gradually into the free arms. 



Horizon and localities.— -Jjo^wer Carboniferous, Chouteau 

 limestone : Sedalia. 



