18 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



in their natural condition are shown, some with as many as 12 inter- 

 nodals, wliich were probably from the distal portions. Among these 

 fragments also are shown some good examples of the form and ])ro- 

 portions of the nodal cohimnals, and of the cog-like processes, as 

 above indicated. 



Sections of stem from near the root are found having strong 

 radicular cirri more or less radiately arranged; and in two instances, 

 clearly belonging to this genus, a cirrus appears in place of one of 

 the cog-like processes, which suggests the idea that these outgi-owths 

 of the nodal columnals are analogous to cirri. 



Lyon observed this peculiar type of column, and gave a description 

 of it, with a figure, in his paper of 1869 in the Transactions of the 

 American Philosophical Society (p. 451, pi.. 26, fig Ji); but with the 

 terms he used his descri])tion is rather hard to understand. 



There is in the species of this genus a marked instability in the 

 form and proportions of some of the principal calyx plates, as well 

 as in some otlier characters. There is much variation in size of the 

 radials, brachials, and intc-rbrachials, not only among dift'erent speci- 

 mens of the same species, but also among the different rays of the same 

 specimen, so that the relative shape and size of these plates are of 

 little value in the definition of species. Even in some of the best 

 defined and most constant Onondaga species, such as D. spinosus, 

 we find the conspicuous first interbrachial undergoing change from 

 broadly truncate above to elongate and almost acuminate, without 

 apparently affecting any of the other characters; and in D. lacus the 

 number of interbrachial ranges may vary among specimens otherwise 

 almost counterparts. Many other examples could be cited, including 

 abnormal specimens, rather frequent, especialh^ in Hamilton species, 

 such as those with four rays, with a sixth plate in the radial circlet, etc. : 

 and the instability in these and otlier respects must constantly be 

 taken into account in considering the definition or identification of 

 species of this genus. 



Genotype. — Dolatocrinus lacus Lyon. 



Distrihution.—Onondsiga: Louisville area, and Ohio ; perhaps Helder- 

 bergian, Tennessee. 



THE SPECIES OF DOLATOCRINUS. 



In the following discussion of Dolatocrinus and its species there 

 will be frequent reference to a few works for which it may be conve- 

 nient to use abbreviations; these are: 

 Miller and Gurley. Bulletins 4 to 12 of the Illinois State Museum, 1894 to 1897. 



Cited: "Miller and Gurley, Bull. 4, 1894, etc." 

 Wachsmuth and Springer. North American Crinoidea Camerata. Memoirs 



Museum of Comparative Zoology, Harvard, vol. 20, 1897. Cited: "Wachsmuth 



and Springer, N. A. Crin. Cam. 1897." 



