16 



others much smaller; they are pentagonal, hexagonal and hep- 

 tagonal; they are tumid, have radial ridges, and bear upon each 

 upper sloping side a single secondary radial, which in turn sup- 

 ports upon each upper sloping side two tertiary radials. There 

 are twenty arm openings to the vault. 



First regular interradials larger than the second primary 

 radials, very tumid and bearing a small radiating ridge directed 

 toward each adjoining plate; it is followed by two much smaller 

 plates, each of which bears a central tubercle, with a radiating 

 ridge directed toward each adjoining plate; these are followed 

 by a single plate that separates the secondary radials. The 

 tertiary radials come together, and hence there are only four 

 plates in any regular interradial area. 



There are only four plates in the azygous area. The first one 

 is in line with the first radials, fully as large and rather longer, 

 quite as tumid and sculptured in the same manner. It is fol- 

 lowed by two plates that are nearly as long as the second and 

 third primary radials together, each one bears a very strong 



...„ b ^ uiuup, cil Durnngton, lowa, and 



now in the collection of Wm. F. E. Gurley. 



ACTINOCR1NUS PLAGOSUS n. Sp. 



Plate II, Fig. 5, azygous side view of calyx; Fig. 6, crushed 

 specimen, showing the arms. 



Species medium or below medium size. Calyx obconoidal, 

 moderately truncated below, wider than high; plates thin, sur- 

 face ornamented with delicate radiating ridges or mere stripes 

 that show slight sculpturing. Vault and proboscis unknown. 



