wHiTEAVES.] DEVONIAN FOSSILS, MACKENZIE RIVER BASIN. 239 



AcTiNOPTERiA BoTDii, Conrad. (Sp.) 



Ai'icula Boydii, Conraii. 1842. Jour. Ac. Nat. Sc. Phil., vol. VIII, p. 237, pi. xii, 



fig- 4. 

 Amcula quadrula, Conrad. 1842. lb., p. 243, pi. xiii, fig. 5. 

 Pterinea Boydii, Conrad. S. A. Miller. 1877, in Cat. Am. Pal. Foss., p. 201. 

 Actinopteria Boydi, Plall. 1884. Pal, St. N. York, vol V, pt. 1, p. 113, pi. xix, 



fig. 2-24, 2(i-30, and pi. Ixxxiv, figs. 16 and 17. 



Athabasca Elver, fii-st ten miles below the mouth of the Clearwater, 

 Dr. E.Bell, 1882: one imperfect but well preserved and character- 

 istic left valve. 



Ptychopteria .equivalvis. (N. Sp.) 

 Plate 32, figs, fi and (ia. 



Shell of medium size, equivalve, rather strongly convex in the nm- 

 bonal region, the umbonal convexity in each valve extending to the 

 anterior end of the base, abruptly inflected into the anterior wing and 

 narrowing much more gradually into the posterior alation : greatest 

 thickness a little more than half the maximum length. Height and 

 length very nearly equal, the greatest length being at the hinge line, 

 whence the valves narrow downwards to the somewhat pointed basal 

 margin, which is narrowly rounded on its anterior side but much more 

 broadly convex posteriorly. Anterior wing comparatively large and 

 distinctly angulatcd at its outer extremity : posterior wing about twice 

 as long as the antejior, not separated from the central portion of the 

 valves by any alar groove or plication, but consisting of a mere up- 

 ward expansion of the post-umbonal .slope, its fiuter termination nearly 

 rectangular but very slightly jiroduced. Cardinal area very narrowly 

 p3'riform in fi-ont of the beaks and linear lanceolate behind them. 

 TJmbones prominent, i-athor broad, and placed a little in advance of 

 the midlength, beaks curved inward, downward and a little forward. 



Surface marked by extremely numerous and minute radiating im- 

 pressed lines or narrow grooves. On the umbonal region and posterior 

 wing some of these grooves are corapaj atively coarse and distant, with 

 much finer ones intercalated between them, but on the anterior wing 

 all the radiating grooves aieof nearly uniform size and very closely 

 disposed. On the anterior wing also the radiating grooves are crossed 

 by very minute but distinct and close set concentric I'aised lines, which 

 are absent on the umbonal region or central portion of the valves and 

 very feebly developed on the posterior wing. 



