"26 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



19 or 21 arms, or one of D. multibmchiatus 37 or 43, that would not 

 make them different species, since the general m.orphological condi- 

 tion would remain the same. It is even true that in some groups 

 species are marked hy increase in the number of arms occurring in 

 less than all the rays, as in Agaricocrinus and Megistecrinus, where 

 the arms may be variously grouped, yet the groupings are according 

 to a definite plan, having a certain relation to the bilateral symmetry 

 of these crinoids. But it is in forms of simple construction like 

 Delatocrinus , when the change in number of arms from 10 or more 

 to 20 or less is effected b}" the addition or subtraction of one or two 

 arms in one or more rays at random, without any definite order or 

 system, and tliis in forms otherwise similar, that such differences 

 must be wholly disregarded in the definition of species. 



The crinoids from Louisville and vicinity of Onondaga age have 

 been derived chiefly from rocks exposed at the Falls of the Ohio 

 River which lie below the hydraulic limestone, being of a formation 

 •of crv^stalline limestone 20 to 30 feet thick, now known locally as the 

 Jeffersonville limestone. Those of the Hamilton are from the upper 

 part of a limestone formation, 8 feet thick, called the Sellersburg 

 limestone, of which the most productive exposures are along Silver 

 Creek in Clark County, Indiana, above the hydraulic limestone. 

 Bear Grass Creek on the Louisville side was in former years a well- 

 known localit}^ for Hamilton crinoids, from which many fine speci- 

 mens were obtained by the early collectors. For a lucid account of 

 the stratigraphy and local occurrences of the region see Dr. R. S. 

 Bassler's paper of 1908 on The Nettleroth Collection of Invertebrate 

 Fossils." For convenience I use the expression "Louisville area" to 

 designate the general locality, including the Falls of the Ohio and the 

 exposures on both sides of the river at Louisville, and along Silver 

 Creek in Clark County, Indiana. 



The relations of the recognizable species are shown by the sub- 

 joined analytical ke5'^s, the Onondaga and Hamilton species being 

 treated separately. Following these I have listed the species for the 

 respective formations with the synonyms under each. The number 

 of species is thus reduced to 12 for the Onondaga and 23 for the Ham- 

 ilton. To avoid needless repetition, it should be noted that the 

 types of Miller and Gurley's species (except three that were lost) are 

 in the Walker Museum at the University of Chicago, and those of 

 Rowley are in the American Museum of Natural History in New 

 York; and that all the species described by both these authors are 

 from Louisville, Kentuck}', and vicinity. The types of Hall are in 

 the American Museum; those of Miss Wood in the United States 

 National Museum; and those of Lyon, Barris, Wachsmuth and 

 Springer, as well as the new material here figured, are in the 

 author's collection, now in the L^nited States National Museum. 



" Smithsonian Miscellaneous Collections, vol. 52, p. 2, pp. 121-152. 



I 



