Remarks on the Trenton Limestone of Kentucky. 151 



basals, the fifth small, pentagonal, and resting upon the upper sloping, 

 right surface of the first azygous plate as in Hyhocrinus. 



Of these radials, the one opposite the upper azygous plate, and the 

 one on either side of it bear arms. The other two are flexed inward 

 above, to meet the plates forming the vault or oral surface of the body. 

 They are centrally excavated by a vertical groove, which is continued 

 downward into the basal plates, and which joins the arm-furrows in 

 the center of the vault. The central portion of these plates, adjacent 

 to the grooves, is so raised as to forma prominent ridge which becomes 

 less elevated below. The}' are covered in \)y a series of small plates, 

 having the same arrangement as the homologous ones of the arm- 

 furrows. The precise relation of the radials to the vault-pieces can 

 not be determined from the specimens. They are all more or less 

 tumid in the center. 



Azygous Plates — Two, the lower hexagonal, alternating with the 

 basals, and forming the fifth plate in the ring with the four large 

 radials. It supports upon its upper right side the fifth radial, and 

 upon the left, the second and smaller azygous plate, which is quad- 

 rangular, about equal in size to the adjacent small radial, and not so 

 large as its homologue in specimens of Hyhocrinus of equal size. 

 The upper surface is not so rounded, nor is it crenulated as in the 

 latter genus. 



Arms — Three, composed of a single row of plates, apparently about 

 as wide as high, very deeply excavated on the inner side by the am- 

 bulacral farrows, which are covered in by a closely interlocking series 

 of small plates having the same arrangement as those of the two radial 

 grooves above described. In transverse section, as may be seen from 

 figs. 1, arid Ic, the arms are found to be appressed lateralh^, so as to 

 give them a flattened appearance. There are no certain evidences of 

 pinnulse. A more or less obscure furrow is seen upon their outer 

 surface, of which nothing further is known. 



Vault — This was evidently covered in by a series of plates between 

 the ambulacra, with the exception of a small space at the inner base 

 of the azygous plate. Their arrangement can not be determined. The 

 small, valvular, anal aperture, is situated upon this side of the ambu- 

 lacral opening, in the line uniting the mouth and the center of the 

 azygous plate, and about half way between it and the inner edge of 

 the open vault space. 



Column — This was round, comparatively small, excentrically situ- 

 ated, as in Hyhocrinus^ and composed of equal, thin segments. 



Remarks — The fossils for which the above generic and specific 



