514 PALAEONTOLOGY OF ILLINOIS. 



from the middle toward the periphery, around which they 

 are each extended for some little distance ; all sinistral, ex- 

 cepting the right posterior one, which curves to the left, 

 with its outer half extending around within that of the 

 next one on the left, near which it terminates at the so- 

 called ovarian protuberance; each composed of two zigzag 

 rows of very small pieces, with some irregular ones appa- 

 rently not belonging properly to either row. Disc com- 

 posed of large, thin, irregular, strongly squamose or im- 

 bricating plates, the imbrication being inward from the 

 periphery, that is, the inner edge of each plate laps upon 

 the outer edge of the next within. Ovarian l pyramid 

 situated near the left outer margin of the posterior inter- 

 brachial space, and closed by ten pieces, apparently imbri- 

 cating laterally, and forming a depressed cone, around the 

 base of which there are numerous small, short, but com- 

 paratively wide imbricating disc plates. Surface minutely 

 granular. 



Greater diameter of an apparently distorted specimen, 

 1.70 inches. 



The only specimen of this species we have seen is somewhat crushed 

 and distorted, so that it is rather difficult to make out the exact details 

 of the structure of the rays, though they are apparently not provided 

 with open ambulacral furrows, the rows of minute plates on each side, 

 apparently closing up and interlocking. There appear, however, to be 

 pores arranged along them in a zigzag row between the pieces. The 

 body plates around the margin are much wider than high, and strongly 

 imbricating upward. No central opening is visible. 



On comparing this species with A. KasTiaskicnsis, Hall, (the only 

 other known Carboniferous species,) the type of which is now before us, 

 we find that our species differs in the important character of having its 

 disc plates all very distinctly imbricating, while those of Prof. HALL'S 

 species show no tendency to imbricate, the whole surface of each being 

 clearly exposed, their straight edges being merely joined together like 

 those of a true crinoid. From Prof. HALL'S description, it might also 

 be supposed that this species differs, in the number of its rays, as he 

 described it as having six rays. A careful examination, however, of 

 the typical specimen has clearly satisfied us that this is certainly not 

 the case, as it has only five, the usual number, as represented in the 



