328 PALEONTOLOGY OF ILLINOIS. 



generally smaller than the other), and is placed with its longer axis 

 nearly so as to coincide with that of the body of the Crinoid. In some 

 species it is more or less dilated at the upper end, while in others it is 

 contracted at both ends, so as to present, as above stated, the form of 

 the shell of a BuUa. It has apparently no colnmella, but is more or 

 less loosely convoluted, with a spiral ridge descending the interior, and 

 sometimes another ascending the exterior. Its walls are generally of 

 moderate thickness, but they often appear to be thicker than natural, 

 in consequence of the presence of inorganic incrustations of calcareous 

 or silicious matter, which also disguise its real struct lire. 



In BatocrinuN VerucnUiainix, t Shumard, this body is narrow below, 

 and sub-cylindrical above to the top, which is slightly dilated. The 

 small opening at the lower end has a thickened rim, which passes 

 around spirally, so as to ascend the outside, as a rather stout ridge, all 

 the way to the top, making nearly two turns, and apparently also form- 

 ing a rim partly around the top. The surface of the whole organ, as 

 well as of its external spiral ridge, has the usual rough appearance,' 

 and when fragments of it are held up, so as to be examined by trans- 

 mitted light, through a good pocket-glass, it is seen to be composed of 

 a great number of very minute polygonal pieces, varying somewhat in 

 form and size. When these pieces are examined under a magnifier, by 

 reflected light, they show shining facets, like crystals, though they are 

 evidently not surface incrustations, but actually compose the walls, or 

 substance of the organ itself. No pores or meshes were observed pass- 

 ing through the walls of this organ in this species, in which it appears 

 to be more than usually dense. 



In another specimen in Mr. WACHSMUTH'S collection, apparently of 

 Actinocrinus proboscidiaUs, * this organ, as seen with one or more of the 

 outer turns removed, lias an oval or subelliptic form, being contracted 

 and twisted at both ends, so as to present very nearly the appearance 

 of the shell of some species of Ovulum. Its walls are quite thin, and 

 seem to form more convolutions than in any other species in which we 

 have had an opportunity to examine it. As seen by the aid of a mag- 

 nifier by transmitted light, it presents a very beautiful appearance, 

 being composed of a great number of minute pieces, with numerous 

 openings passing through between them. The little pieces and the 

 openings between them are of nearly uniform size, and arranged so 

 that there are usually one or two of the former intervening between 

 any two of the openings. 



Another of Mr. WACHSMTJTH'S specimens of Actinocrimts securls, 

 Hall, has one side of the body removed so as to show about two- 

 thirds of the convoluted organ, the upper part of which is broken 



* See plate 9. fig. 7. f See plat* 9, fig. 13. 



