MORPHOLOGICAL PART. 143 



seem to have been obscured by heavy incrustations of silicious matter at 

 both sides, and these incrustations may have produced the apparent dupH- 

 cation of the walls (Plate Y. Figs. 1, 4, 9, and 12). 



Among the many beautiful examples in the Wachsmuth collection at the 

 Museum of Comparative Zoology, in which the convoluted organ is pre- 

 served, there are two unique specimens (Plate V. Fig. 11 and Fig. 10) ; the 

 former showing the delicate porous texture, the other its position beneath 

 the ambulacral skeleton. The collection contains also the remarkable speci- 

 men of Macrocrinus verneuilianus (Plate V. Fig. 8), in which the upper end 

 of the organ is surrounded by a large annular vessel with five radial and five 

 interradial openings. In this species the end of the outer fold turns into 

 a narrow thickened strip, which ascends spirally toward a place in the 

 direction of the anal tube. This structure differs somewhat from that of 

 Teleiocrimis and other genera which have a thickened edge along the lower 

 margin of the outer fold passing upward (Plate V. Figs. 1, 3, 12). In a 

 specimen in our collection, either o? Strotocrinus or Teleiocrinus, we succeeded 

 in removing at one side the two outer folds, and exposed the third or inner 

 fold (Plate Y. Fig. 4), which has the form of a spindle, thicker at the middle 

 and tapering to both ends. It seems that the innermost cavity in all cases is 

 spindle-shaped, and that the inner end winds spirally upwards like a screw 

 with rather sharp, roughened edges, — the so-called ^'collar" of Meek and 

 Worthen. A connection with the ambulacra has not been satisfactorily 

 observed in the specimens ; neither the upper part of the organ, nor the 

 ends of the ambulacral tubes, have been found in perfect preservation. 



The function of the convoluted organ can only be conjectured, as no 

 similar structure has been observed in recent Crinoids ; but from its position 

 it seems probable that it was connected with, or formed a part of, the 

 digestive apparatus. If the latter was the case, the thickened outer end, 

 leading toward the anus, may represent the hind gut. 



