Bemarks on the Trenton Limestone of Kentucky. 149 



aDces are numerous, and often marked on the surface by corresponding 

 elevations and depressions. It is possible, though not without severe 

 labor, to work out the lower part of this section in various directions, 

 as numerous tributaries, of greater or less size, have excavated the 

 limestones to the level of low- water of the Kentucky river. These afford 

 means of reaching all parts of the formation, and obtaining satisfactory 

 collections of its fossils. To the kindness of Hon. Jno. K. Procter, now 

 director of the Geological Survey of Kentucky, I am indebted for sug- 

 gestions as to the distribution of the Trenton, as the surface formation 

 in his "Siluro-Cambrian" area of Central Kentucky, as well as for in- 

 formation respecting its appearance and fossils at Frankfort. The area 

 marked as Trenton on this map by Prof. Procter, diff'ers very much at 

 the north from what is indicated by this paper, as the first outcrop of 

 this formation in that direction, is made to fall between Nicholasville 

 and the Kentucky river. If this determination rested upon the fossils 

 alone, without consideration of the change in topography and the litho- 

 logical character of the strata, perhaps nothing would be doubtful, and 

 even as it is, I wish, in acknowledging Prof. Procter's kindness, to say 

 that this paper is to be regarded as suggestive respecting this part 

 of the formation, rather than otherwise, or as being a finished determin- 

 ation. I am, however, personally convinced that the evidences are all 

 in favor of these suggestions, and have little expectation that future 

 studies will alter my conclusions. The collection of Echinoderma 

 enumerated in the list above given is a remarkable one. It embraces 

 not only several of the rarest Crinoids and Cj^stideans known, but also 

 those of the most anomalous characters, and of the greatest interest, 

 as blending an assemblage of structural peculiarities in one organism, 

 that were finally diff'erentiated into several distinct forms. Among 

 these was the Blastoidocrinus car char ideus^ Billings, now first found 

 in such a condition as to determine the proper relations of its parts, 

 relations predicted with much accurac}^ from the merest fragments, 

 by that astute palaeontologist. The new fossil, which I have called 

 Hyhocystites problematicus, is the first found which so closely unites 

 characters both of the Crinoidea and Cystoidea, with the reference of 

 the former characters to those of an undoubted Crinoid of very near 

 relationship. I feel that the special attention of all earnest students of 

 the fossil Echinoderma should be especially called to the extraordinary 

 characters of this genus, and its close resemblance, in many of these, 

 to IlybociHnus, Billings, an undoubted Crinoid ; a resemblance so 

 striking that the sexual question is at once suggested as between the 

 two. 



