1869.] MEEK AND WORTHEN — ON i>aL^ozoic! crinoidea. 439 



performed in the internal economy of these animals. In the second 

 volume ot the Illinois Geological Reports, published soon after 

 we figured, on page 191, a specimen of Strotocrinus, with this 

 body seen in place, and stated that we regarded it as having 

 been connected witli the digestive apparatus of the animal. 



Both in Prof. Hall's and our own remarks, this organ was 

 spoken of as a convoluted plate. This, however, we now know is 

 not strictly correct, for although composed of hard calcareous 

 matter, and in some species somewhat dense in structure, it seems 

 to be always constructed of a great number of minute pieces, and 

 generally has a more or less open or porous texture ; while in 

 some cases it presents the appearance of an exceedingly delicate 

 net-work. It seems never to be attached to the bottom of the 

 visceral cavity, though it extends down nearly to the bottom. It 

 is open at both ends (the opening at the lower end being 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 leas 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 Bulla. It has apparently no columella, 

 but is more or less loosely convoluted, with a spiral ridge descend- 

 ing 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 structure. 



In Actinocrinus Verneuiliamcs, 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 apparentlv also forming ,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 transmitted 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 



