ECHINODERMATA—CYSTOIDEA. 



473 



31. A. (Lepidodiscus) squamosus Meek and Worthen. Mississippic. 

 Disc plates imbricating. Ambulacra, four sinistral and one dex- 



tral. Differs from A. cincinnatiensis in its larger size and in the 

 lateral position of the anal aperture in its interradius. 

 Keokuk of Indiana. 



32. A. (Discocystis) kaskaskiensis Hall. Mississippic. 

 Disc plates not imbricating, smooth. Ambulacra very long and 



narrow. 



Kaskaskia of Missouri and Illinois. 



XVII. Hemicystites Hall. 

 Like Agelacrinus but differs in its much smaller size and straight 

 and proportionally wider ambulacra. Ordovicic-Siluric. 



/■- 



Fig 1784. a, He^nicystites stellaitis, top view, X 2 ; r, H. granulatiis, side view, 

 X 2 ; ^ (center), Agelacrinus cincinnatiensis, X 2. (After Me*k, Pal. Ohio.) 



33. H. stellatus Hall. (Fig. 1784, a.) Ordovicic. 

 Discoidal, subpentagonal. 



Cincinnatian of Cincinnati region. 



34. H. granulatus Hall. (Fig. 1784, r.) Ordovicic. 

 Calyx elevated into a cylindrical form and covered by numer- 

 ous grain-like pieces. Usually grows on Strophomena. 



Cincinnatian of Cincinnati region. 



XVIII. PoROCRiNus Billings. 

 Calyx conical, with five pentagonal plates in the basal cycle 

 (infrabasals) ; three hexagonal and two heptagonal in the second 

 cycle (basals) ; six in the third row (five radials and one in- 



