346 PROCEEDINGS OF THE ACADEMY OF [1888. 



Plate XVIII, figs, 4, 8, 9, 10, 15, except that they do not meet in the 

 center, but leave a slightly excenti'ic, obtusely pentagonal oral opening, 

 transversely elongated, its longest side next to the posterior oral plate. 

 Into this opening, which is deep, and contains at the bottom some 

 dark-colored substance, converge the ambulacra, their lips turning 

 downward at the five corners. They enter between the five plates, 

 touching them, and completely separating the visible portions of 

 those plates from each other. Whether there is any lateral projec- 

 tion beneath the ambulacra, by which they come in contact again, 

 cannot be seen, but from the form of the exposed portions we should 

 think not. 



That the five plates around the center, although somewhat unequal 

 in size, represent the five orals of the recent genera Rliizocrinus, 

 Hyocrintis, and Holopus, and that the integument of small pieces is 

 a disk and not a vault, nobody will deny after seeing the specimen. 

 And a comparison of the parts in Taxocrinus with the summit plates 

 in Platycrinus, Actlnocrinus, etc, leaves no room for doubt that these 

 are likewise orals. In the posterior interradius (PI. XVIII, fig. 1, 

 c), there is a small lateral appendage or proboscis composed of a row 

 of rounded quadrangular plates gradually tapering upward. This 

 appendage is supported by a small anal plate, which rests upon the 

 right upper corner of the posterior basal and the right posterior 

 radial, both of which are somewhat indented to receive it. The ap- 

 pendage seems to be attached by its inner side to the integument, and 

 there are to the right of it, within the posterior interradius three 

 small tapering ridges composed of very small plates, which look like 

 branches from it; upon close inspection, however, they are seen to be 

 folds in the perisome, into which they are incorporated at their upper 

 ends, in a similar manner as the row of larger plates. At the upper 

 end of the appendage there are a great many minute pieces closely 

 packed together, and we think it probable there was an opening at 

 this point. In the two other specimens (PI. XVIII, figs. \h, and Id), 

 the structure is more clearly shown. Xeither of them has supple- 

 mentary ridges or folds, and it is plainly seen thai the large plates 

 composing the proboscis are. bordered by numerous small pieces, by 

 means of which they are connected with, or incorporated into the 

 perisome. The upper end of the appendage is rounded off", and stands 

 well out from the perisome, but we have been unable to ascertain 

 ' from the specimens whether it is perforated by a canal, or solid as in 

 the remarkal)le recent genus Thaumatocrinus, Avhich in the structure 



