Carboniferous Rocks of the Mississip/d Valley. 281 



This species differs from all others of the genus in the 

 form of the basal part, but principally in the dome, which 

 has not tuberculous plates, as usual in this group. In the 

 small, smooth dome plates it is somewhat related to Acti- 

 nocrinus brevis, (Iowa Geol. Rep. pi. 10, fig. 3, and when 

 the dome only is seen it might easily be mistaken for that 

 fossil ; but in the characters of the basal portions it is very 

 distinct. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collections of C. A. White and 

 Dr. O. Thieme. 



Ag-aricocrinus (Amphoracrinus) bellatrenia (n. s.). Body 

 broadly cyathiform, saucer-shaped, sometimes nearly flat 

 to the extent of the third radial plates, somewhat protrud- 

 ing on the anal side ; dome elevated. Basal plates small, 

 concealed in a moderate depression for the attachment of 

 the column. First radial plates variable in size, broader 

 above than below. Second radial plates quadrangular, 

 twice as wide as high. Third radial plates broad, short, 

 pentangular, succeeded on each upper side by two or more 

 short, broad plates, from which arise the free arms. 



First interradial plates large, mostly ten-sided, sub-oval, 

 supporting two narrow, elongate, secondary interradial 

 plates, which reach to the arm openings. First anal plate 

 heptagonal, supporting three slightly smaller plates in the 

 second range, with numerous plates above. Dome plates 

 various in size, some strongly tuberculous, the terminal 

 one largest ; those bordering the anal opening are small ; 

 those of the next range beyond are large, and produced 

 into strongly elevated tubercles, and, in old specimens, 

 sometimes becoming sub-clavate. 



This species differs from any other, except A. convexns, 

 in the greater convexity of the base, while the peculiarly 

 ornamented anal area distinguishes it from every other. 



There are in the collections eight specimens, the smallest 



JOURNAL B. S. N, U. 36 JANUARY, 1861. 



