ACTINOCRrNID^. 641 



rays. Arms comparatively short, and rather delicate ; slightly flattened at 

 the npper ends. Regular interbrachials : 1, 2, 2, followed by 2 and 1 plate 

 within the rim; the latter piece arched over by the plates of the proximal 

 pinnules of the proximal arms in adjoining rays ; the anal interradius con- 

 sists of 2, 3, 4, 2 and 2 plates. Interdistichals one, roofed by the incorpor- 

 ated lower pinnules of the second arm. Tegmen rising but slightly at the 

 top of the rim, the middle portion low dome shaped ; the plates very 

 numerous, irregularly arranged, nearly flat, gradually decreasing in size 

 toward the arm bases. Anus subcentral, at the top of a small protuberance. 



Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa, 

 and at several places in Missouri. 



Type in the (Worthen) Illinois State collection. 



Remarks. — This species differs from the preceding one in the smaller 

 size, the shortness of the calyx, the less number of arms, and in the convexity 

 of the ventral disk. 



