14 SMITHSONIAN INSTITUTION 



new species, S. pybumensis. The former is remarkable for its extraordinary 

 size, being among the largest of known crinoids; and in both is presented a 

 new phase of crinoid morphology, in that the calyx is lobed by the protuberance 

 of the interradial areas instead of the radial. Some of the specimens are very 

 well preserved as to the calyx, and show the fixed pinnules of the interbrachial 

 pavement more plainly than is seen in the Cape Girardeau species. A third 

 species, S. mutabilis, of the elegans type, is well represented, and it also occurs 

 in Perry County and other localities to the north. The associated Camaro- 

 crinus bulbs and Scyphocrinits calices in this new material confirm most beauti- 

 fully the observations before made as to the relative size of the stem at the 

 proximal and distal ends, as will be shown further on. All these occurrences 

 are in the Ross limestone of the Linden formation (Helderbergian), which has 

 a thickness of more than ioo feet in two principal Hardin County areas, 

 Pyburn's Bluff on the Tennessee River and Horse Creek to the eastward. There 

 are several beds of white, blue, and cherty limestones. The great Camarocrinus 

 clay bed is included within a series of white limestones in the lower part of the 

 formation in the Horse Creek area ; these are followed by about 60 feet of hard 

 bluish- to yellowish-brown cherty limestones, disintegrating occasionally into 

 clay pockets, and in the upper 25 or 30 feet of these cherts is found the 

 S. pratteni. S. pybumensis occurs at the Pyburn Bluff area through about 

 35 feet of bluish-grey and cherty limestones, in the lower part of the formation 

 down to the water's edge. Here the pratteni beds are not exposed, and the two 

 species are not found in the same horizon or locality. S. mutabilis occurs in 

 both areas, probably concurrent with the other two species. 



So far as observed, the crinoids, both Camarocrinus bulbs and other 

 remains, occur rather indiscriminately throughout their respective limestone 

 and cherty strata, and not in a single clearly defined horizon as in the lower 

 clays. 



CONSTRUCTION AND PROBABLE ORIGIN OF THE BULBS 



Before proceeding to consideration of the species, it may be well to present 



the result of studies upon the mechanics of these singular root structures. 



Schuchert's description, slightly condensed (op. cit, pp. 263-264), is as follows: 



Inside of the bulb is a large, more or less pentagonal, medio-basal chamber, around 

 which are usually arranged five or six, and more rarely as many as 11, variously shaped 

 chambers. The walls of the camarae have their origin in bifurcations of the roots beneath 

 the stalk. The walls of the chambers are double, and are made up of small, irregularly 

 shaped plates. Each lobe has a large opening leading to it from the axil of a root 

 bifurcation. The inner walls are surrounded by an outer integument of innumerable small 

 plates, devoid of regular arrangement. The origin of this outer wall is independent of 

 the roots. At the stalked end of the bulb is a projecting collar which bounds the area 

 occupied by the visible parts of the branching roots. Around the inner side of this collar, 

 and in the forks of the last visible bifurcations of the roots, are the openings into the 



