180 PALEONTOLOGY OF ILLINOIS. 



FAMILY MODOCRINID.E. 



GENUS RHODOCRINUS. 

 KHODOCRINUS KIRBYI (nov. sp.) W. & Sp. 



PL XV, Fig. 10. A specimen with infolded arms, and column. 



PL XVI, Fig. 3. Another specimen with spreading arms, showing the pinnules. 



This species is characterized by its barrel-shaped calyx, robust 

 arms for the genus, short arm joints, and rapid widening of the 

 arm bases up to the first bifurcation. The color of the speci- 

 mens is very dark. 



Calyx elongate, truncate below; the sides nearly straight, 

 swelling but little from the lower edge of the basals on which it 

 rests to the top of the third radials, above which it contracts 

 rapidly, producing the form of a barrel. Some specimens are 

 almost cylindrical, about equal in diameter at top and bot- 

 tom. Viewed from above or below, the outline is obscurely pen- 

 tagonal. 



Base sharply impressed. Underbasals small, resting in a shallow 

 concavity concealed by the column. Basals very large, their 

 lower margins sharply bent inward, forming the edge of a rim 

 on which the cup rests. Sutures distinct. 



First primary radials much smaller than the basals; the 

 second and third about half as large as the first, and equal to each 

 other. Secondary radials 2x2x5, quadrangular, narrow, rising 

 above the surface in prominent ridges, which increase in width 

 upward. They are succeeded by three very short, transversely 

 arranged brachials, which also successively widen upward. The 

 upper one is axillary, giving off two branches. The inner branch 

 of the rays bifurcates again, generally on the third plate, thus 

 giving three arms alternately arranged to each main division 



