Descriptions of Neiv Species of Crinoidca. 261 



Art. IV. — Descriplions of New Species of Crinoidca front, 

 the Carboniferous Rocks of the Mississippi Valley. By 

 James Hall. 



[Read Dec. 19th, I860.] 

 GENUS ACTlNOCIilNUS. 



Actinocrinus leucosia (n. s.). Body depressed-turbinate, 

 broadly trmicate at base ; dome moderately elevated, 

 surmounted by a central proboscis. Basal plates pro- 

 jecting as a salient trilobed rim, slightly excavated for the 

 attachment of the column. Radial series large, first ra- 

 dial plates more than once and a half as wide as high ; 

 second radial plates quadrangular, twice as wide as high ; 

 third radial plates broad, pentangular, supporting on each 

 upper inclined side a double range of short, broad, supra- 

 radial plates ; the upper one of each series is a bifurcating 

 plate, and supports on each side a double set of brachial 

 plates, giving four arms to each ray, except in the anterior 

 ray, where there are two arms, making the brachial for- 

 mula ij =: 18. 



Interradial series consisting of from three to five plates 

 each ; the first large, eight or ten sided, supporting two in 

 the second range, and two in the third range, where there 

 are five in the series. First anal plate heptagonal, equal 

 to the first radial plates in height, but much narrower ; 

 supporting three smaller plates in the second range, with 

 several smaller plates above, the number and arrangement 

 not determined. Surface of plates moderately and regu- 

 larly convex, without ornament. 



Arms strong, simple, composed of a double series of 

 short, broad plates, very obtusely wedge-form at the inter- 

 locking edges. Dome composed of numerous small tu- 

 berculose plates ; somewhat lobed by depressions corre- 



JOUHXAL B. S. N. II. .I.\XI AKY. 18G1. 



