Carboniferous Rocks of the Mississippi Valley. 273 



support, on the anal side, a supra-radial bifurcating plate, 

 on each side of which rests a brachial plate ; and on the 

 other side a single brachial plate, giving three arms to 

 each, raakinof the brachial formula 52 =: 12. 



First interradial plates comparatively large, ten-sided, 

 supporting two elongate plates in the second range. 

 First anal plate heptagonal, as large as the first radial 

 plates, supporting three smaller plates in the second range ; 

 the two lateral ones eight-sided, a little smaller than the 

 first interradial plates ; middle one smaller, five-sided. 

 The third range of anal plates consists of three small 

 ones, above which they are not determinable. Surface of 

 plates of the radial series marked by angular nodes, and 

 ridges leading from these to join with the low radiating 

 ridges of the first interradial plates. Arms comparatively 

 large, composed of a double series of interlocking plates. 



This species differs from any other described in the pe- 

 culiar flat base and angular sides ; the cup resembling a 

 low, broad-bottomed, pentangular basket. Notwithstand- 

 ing the flatness of the base, it is not of the type of Agari- 

 cocrinus, Troost, or Ampkoracririus. 



Geological formation and locality. Burlington lime- 

 stone. Burlington, Iowa. Collection of C. A. White. 



Actinocrinus desideratus (n. s.). Body elongate, sub- 

 cylindrical, obconic; dome depressed-convex, and armed 

 on the margin by five strong spines, one over each pair of 

 arms. Basal plates unknown (apparently they were very 

 large). First radial plates large, higher than wide. Sec- 

 ond radial plates small, quadrangular, wider than high. 

 Third radial plates small, larger than the second, nearly 

 twice as wide as high, wedge-form above, and supporting 

 in the anterior and antero-lateral rays the brachial plates, 

 only one of which contributes to form the body, while in 

 the postero-lateral rays they support on each side a supra- 

 radial bifurcating plate, on each upper edge of which rests 



JOURNAL B. S. N. U. 35 JANUAKY, ISGl. 



