CRINOID GENUS SCYPHOCRINUS 47 



(and possibly pinnulars and interpinnulars) to the height of the arm-bases; 

 thus the interbrachial spaces appear thickly studded with the spines, which 

 diminish in size upward. There is a certain uniformity of direction in which 

 numbers of adjacent spines lie in clusters which leads to the conclusion that 

 they were articulated; this is confirmed by the appearance of the small, elevated 

 centers of the plates, which look like sockets, and by the proportions of the 

 spines themselves. The usual fixed spines, developed from pustulose growths 

 upon the plates, are broadest at the base, from which they taper conically; 

 whereas these are narrow at the base, cylindrical for the greater part of their 

 length, after which many of them expand or branch. 



The species is represented by a single specimen in a remarkably good con- 

 dition, all the structures being sharply preserved. In the part originally 

 exposed only a few of the smaller spines were visible in the upper inter- 

 brachial region (PI. IX, fig. ic). But careful cleaning from the rather hard 

 matrix brought to view not only the fringe of long spines lying parallel in 

 clusters at either border of the same side, but also a good part of the opposite 

 side of the specimen, on which a forest of spines lie in place to the level of the 

 upper secundibrachs (PI. IX, fig. ib). On this side also the sharp sculpturing 

 of the lower calyx plates is beautifully shown. 



The presence of articulated spines in this isolated species of so prolific a 

 genus is a most remarkable occurrence, suggesting comparison with the other 

 Devonian form, Arthracantha, in which the character seems to be constant for 

 all the species. The branching or distal enlargement in our species is, however, 

 a development for which no parallel is thus far known among the crinoids. In 

 view of the fragile nature of these structures, and the impediments to their 

 preservation in the fossils, it is quite possible that some of the other species may 

 have possessed similar spines ; for example, 5". stellatus, and the species repre- 

 sented by the fragments from Benton County, Tennessee (figured on PI. VI), 

 in which the sculpturing is very similar. 



Type. — The holotype is in the author's collection. 



Horizon and locality. — Helderbergian ; Ross limestone of the Linden for- 

 mation, Hardin County, Tennessee. 



3. SCYPHOCRINUS MUTABILIS n. sp. 

 Plates VI, figs. 3-19 ; VIII, figs. 3, 4, 5 



A variable species of the elegans group, with strong surface sculpture. 

 Calyx of medium size, usually wider than high, but sometimes slightly elongate : 

 lower part of cup broadly expanding, with sides usually convex, rarely about 

 straight, or slightly concave near the base. Secundibrachs 12 to 15, the upper 

 seven or eight very short and wide; median ridge varying from medium size 



