bo 
MELOCRINID&. 75 
as the free brachials. Arms ten, slender, not bifureating; composed of quad- 
rangular, moderately high joints with long pinnules. Interbrachials: 1, 2, 2, 
2, decreasing in size upwards. The anal interradius considerably wider: 
1, 3, 5, etc.; the middle series longitudinally arranged, and marked by a 
conspicuous ridge. Interdistichals: 1, 2, ete. Construction of ventral disk 
and anus unknown. Column obscurely pentagonal to judge from the top 
joint; the axial canal of medium size.* 
FHforizon and Locality. — Trenton limestone ; Ottawa, Canada. 
Types in the Canada Survey Museum at Ottawa. 
Glyptocrinus marginatus Bitircs. 
Plate XX. Fig. 2. 
1856. Glyptocrinus marginatus — E. Brurxes; Geol. Sury. Canada (Rep. of Progress), p- 260; also 1859, 
Decade LV., p. 59, Plate 9, Fig. la. 
1881. Areheocrinus marginatus —W. and Sp.; Revision Paleoer., Part II., p. 190. 
1859. Archeocrinus marginatus — 8, A. Mitrer; N. Amer. Geol. and Palont., p. 225. 
A large and well marked species. Exact form of calyx undeterminable 
— the only specimen being in a crushed condition — but probably subglo- 
bose. Plates evenly margined by a strong elevated border crossing the 
radial ridges, their middle portions smooth and very thin; the inner floor of 
the plates marked by slender conspicuous tubercles. Radial ridges not very 
prominent, wide and flattened. 
Basals small, projecting laterally. Radials and costals as long or a little 
longer than wide; the former twice as large as the costals. Distichals about 
seven; all, or nearly all, incorporated into the calyx, rapidly decreasing in 
size; the proximal one as large as the costals, and of similar form; the upper 
axillary, and succeeded by free arm plates. Arms delicate, composed near 
the calyx of moderately long (nearly as long as wide), slightly cuneate 
joints. There are apparently no fixed pinnules; the free pinnules long, stout 
at the base, distinctly tapering. Interbrachials: 1, 2, 2, 1, 2, 3, 2, followed 
by others; their five lower ones of nearly the same size as the radials. Anal 
area considerably wider, and composed of a much greater number of plates 
than in any other species of the genus. It contains a middle series of anal 
plates, marked by an obscure ridge, and to both sides of this ridge there are 
numerous interbrachials, arranged like those of the four regular sides, but 
* It is doubtful if the detached column, which Billings found associated with the type specimen, belongs 
to this species. 
