Bemarks on the Trenton Limestone of Kentucky. 153 



radial aur] extending over the suture half wa}^ down the basal, while 

 fig. lb shows the ungrooved radial of Hybocrinus, and the lower joints 

 of the upright arm supported b}^ it. As may be seen from the figure, 

 the upper az3'gous plate of Hybocrinus is rounded and crenulated at 

 its distal extremity, as well as much thickened. 



The form of the plate is suflficient evidence that it supported a strong- 

 ventral sac, and the crenulated condition of the articulating upper sur- 

 face of this plate, indicates the place of the lower exterior openings in- 

 to this sac. In no case is there any evidence of dome or vault-plates 

 remaining in any of the sixteen specimens so far collected. The body- 

 plates were remarkabl}^ thick and heavy, and the upper margin of the 

 radials was so bent inward as to make the vault-space comparativel}^ 

 small. 



This is the first discovery of this genus outside the Trenton of 

 Canada, on record, although it is now twenty-four years since Mr. Bill- 

 ings found it there. 



Lqcality and Position — Mercer county, Kentucky, in the upper part 

 of the Trenton group. Sixteen specimens, referred to H. tumidus-i 

 Billings, and H. conicus, Billings (one specimen). 



Heterocrinus milleki, nov. sp. ' 



(Plate v., fig. 3, symmetrical side, three diameters.) 



Under basals — Not present, or very minute. In the onl}' other spe- 

 cies of this genus closely allied in any of its characters to the one un- 

 der consideration (H. juvems,'!!^}!), the}^ appear only as small trian- 

 gular points at the junction of the basals. In both specimens of this 

 species there is no evidence of their presence. 



Basals — These are so minute, and so blended with the upper ex- 

 tremity of the column, that it is quite impossible to describe them 

 clearly. In both specimens there is an apparent anchylosis of these 

 plates, forming a solid base upon which rests the first ring of the 

 radial series. This character, which is well shown in the figure, would 

 seem to be abnormal or accidental, were it not for the fact that both 

 specimens are exactly alike in this regard. It is a very marked feat- 

 ure of the species, and at once distinguishes it from any other of the 

 genus hitherto described. 



Badials — Five, the three shown, quadrangular, higher than wide, 

 upper and lower articulating surfaces straight and parallel, the plates 

 being slightly wider and thicker at the upper extremity. These plates 

 can only be seen upon the symmetrical side in the specimens studied, 

 and here they are equal in shape and size. The slight widening and 



