Carboniferous Rocks of the Mississippi Valley. 267 



posed of medium sized polygonal plates, some of which 

 are tuberculiform or sub-spiiiiform. 



This species resembles A. corhulis in general appear- 

 ance, but differs in the arm formula, in the less spreading 

 calyx, and the longer tubercles. 



Geological formation and locality. Burlington lime- 

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

 Burlington. 



Actinocrinus rusticus (n. s.). Body broadly spreading 

 to the arm bases, which project in the form of strong 

 lobes; dome depressed-convex, surmounted by a sub-cen- 

 tral proboscis. Basal plates very short. First radial plates 

 proportionally large, wider than high, superior lateral sides 

 long. Second radial plates hexagonal. Third radial 

 plates smaller than the second, pentagonal, twice as wide 

 as high, obtusely wedge-form above, supporting on each 

 upper side a supra-radial bifurcating plate, which on the 

 outer margin supports brachial plates, and on the inner 

 margin supports a supra-radial plate of the second order, 

 which gives origin to two arms, making three to each 

 main division of the ray, and six to the ray, giving the 

 arm formula ^V r=: 30. 



First interradial plate large, hexagonal, supporting two 

 smaller hexagonal plates in the second range, with three 

 or four plates in the third range, situated high up in the 

 brachial spaces. First anal plate hexagonal, smaller than 

 the first radials, sustaining two smaller hexagonal plates 

 in the second range, with several smaller plates irregularly 

 placed above. Surface of the body plates highly tubercu- 

 lose, the tubercles of the basal plates generally much ex- 

 tended. Dome composed of small, polygonal, slightly 

 convex plates. 



This species resembles A. verrucosus., (Iowa Geol. Rep. 

 pi. 11, fig. 7 ;) but differs in being much broader in propor- 

 tion to its height, the dome less elevated, with plates never 



