326 PROCEEDINGS OF THE ACADEMY OF 



of a large convoluted body, resembling in form the shell of a Bulla or Scaphan- 

 der, within the body of several types of the Actinocrinidee, was noticed by Prof. 

 Hall in vol. xli, p. 261 of the Am. Journ. Sci., in 1866, though he made no sug- 

 gestions there in regard to the functions it probably performed in the internal 

 economy of these animals. In the second volume of the Illinois Geological 

 Reports, published soon after, we figured, on page 191, a specimen of Stroto- 

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

 been connected with 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 al- 

 though composed of hard calcareous matter, and in some species somewhat 

 dense in structure, it seems to be always constructed of a great number of mi- 

 nute pieces, and generally has a more or less open or porous texture ; while iu 

 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 ex- 

 tends down nearly to the bottom. It is open at both ends (the openiug 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 less dilated at the upper end, while in others it is con- 

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

 a Bulla. It has apparetitly no columella, but is more or less loosely convoluted, 

 with a spiral ridge descending the interior, and sometimes another ascend- 

 ing 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 Verneuilianus, Shnmard, 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 as- 

 cend the outside, as a rather stout ridge, all the way to the top, making nearly 

 two turns, and apparently also forming a rim partly around the top. The sur- 

 face 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 

 lighl, 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 passing through the walls of this 

 organ in this species, in which it appears to be more than usually dense. 



lu another specimen in Mr. Wachsmuth's collection, apparently of Aclwocri- 

 nus proboscidialis, this organ, as seen with one or more of the outer turns re- 

 moved, has an oval or subelliptic form, being contracted and twisted at both 

 ends, so as to present very nearly the api)earance of the shell of some species 

 of Ovuluvi. 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 magnifier by transmitted light, it presents a very beauti- 

 ful appearance, being composed of a great number of minute pieces, with nu- 

 merous 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 open- 

 ings. 



Another of Sir. Wachsmuth's specimens of Actinocrinu.ssecvrus,\{si\\, has one 

 side of the body removed so as to show about two thirds of the convoluted or- 

 gan, the upper part of which is broken away. The part remaining has a short- 

 wide subcylindrical form, with a rather broad, obliquely truncated lower end, 

 which is not tapering, as in the other species. Under a magnifier it is seen to 

 be composed of an extremelj- fine net-work, far surpassing, indeed, in delicacy 



[Dec. 



