PALEONTOLOGY OF IOWA. 551 



The line of articulation between the first and second ra- 

 dials, and between the second radial and the arm-plates, and 

 also between the plates of the arms, is usually more or less 

 gaping exteriorly, and the edges of the plates rounded, as if 

 the space had been filled with some cartilaginous or muscular 

 substance during the life of the animal. 



The species at present known to me are, two in the Burlington limestone, one in 

 the Warsaw limestone, two or more in the St. Louis liestone, and four or more in 

 the Chester limestone. One species is described by Dr. TKOOST as Jlgassizocrinus 

 gracilis ; the reference to the latter genus having been induced by the imperfect con- 

 dition of the base, by which the characters are obscured*. 



Scaphiocrimis simplex ( n . s .) . 



PLATE IX. FIG. 10. 



GENERAL form of body and arms subcylindrical : calyx 

 shallow, spreading to the upper edge of the first radials. Ba- 

 sal plates minute, and projecting slightly beyond the column. 

 Subradial plates five : four of them pentagonal, with the 

 lateral and superior margins equal ; one hexagonal, being 

 truncated above by the first anal plate. First radial plates 

 short pentagonal, with the upper side much extended. Second 

 radials somewhat pentagonal, wedgeform above, and straight 

 below. Anal plates six, the lower one the larger, and octa- 

 gonal. 



* For purposes of comparison, I subjoin from the work of DE KONINCK and LE HON 

 the generic description and illustrative diagram of GRAPHIOCRINUS. The name was pro- 

 posed to designate a peculiar crinoid from the Upper Carboniferous limestone of Belgium. 



Genus Graphiocrinus ( DE KONINCK & LE HON ). 



"The summit of this genus when complete, is very elongate, nearly cylindrical, and 

 represents very well the form of a pencil or paint-brush : this distant resemblance 

 suggests the name. 



" CALYX short, composed of five small basal lozenge-form pieces, and producing to- 

 gether a five-rayed star : between the rays of this star are placed the five first i&dial 

 plates. These are pentagonal, connected by their lateral edges, and disposed in the same 

 manner as the basal pieces. The second radials are placed vertically upon the first, and 

 connected by their lateral edges, forming a little cup. A single anal plate, of ovoid form, 

 is interposed between two rays, and adjacent to four other pieces which enclose it, and 



