MELOCRINID^. 275 



as the free brachials. Arms ten, slender, not bifurcating; 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, 3, etc.; the middle series longitudinally arranged, and marked by a 

 conspicuous ridge. Interdistichals : 1, 2, etc. Construction of ventral disk 

 and anus unknown. Column obscurely pentagonal to judge from the top 

 joint; the axial canal of medium size.*" 



Horizon and Localiti/. — Trenton limestone ; Ottawa, Canada. 



Tyipes in the Canada Survey Museum at Ottawa. 



Glyptocrinus marginatus Billings. 

 Plate XX. Fig. 2. 



1856. Olyptocrinus marginatus — E. Billings; Geol. Surv. Canada (Rep. of Progress) , p. 260; also 1859, 



Decade IV., p. 59, Plate 9, Pig. la. 

 1881. Archaocrinus marginatus — W. and Sp. ; Revision Palseocr., Part IL, p. 190. 

 1859. Archaocrinus marginatus — S. A. Miller; N. Amer, Geol. and Palseont., 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. Kadial ridges not very 

 prominent, wide and flattened. 



Basals small, projecting laterally. Kadials 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 dehcate, 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 fiYQ 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. 



