BILLINGSELLID^. 727 



stone forming 2b of the Stephen formation [Walcott, 1908f, p. 211]; both on Mount Bosworth, north of the Canadian 

 Pacific Railway between Hector and Stephen, on the Continental Divide between British Columbia and Alberta, 



(57j) About 2,000 feet (609.6 m.) above the Lower Cambrian in the limestone forming 2 of the Stephen formation 

 [Walcott, 1908c, p. 237 (6)], just east of the "fossil bed," on the northwest slope of Mount Stephen, above Field on 

 the Canadian Pacific Railway, British Columbia, Canada. 



lower Cambrian : (58k) Just below the Middle Cambrian in the limestone forming 1 of the Mount Whyte forma- 

 tion [Walcott, 1908c, p. 240 (9)], just above the tunnel; and (58p) drift block of limestone believed to have come from 

 the limestone forming 1 of the Mount Whyte formation [Walcott, 1908c, p. 240 (9)], found near the Canadian Pacific 

 Railway track just west of the tunnel; both 3 miles (4.8 km.) east of Field, British Columbia, Canada. 



NisusiA COMPTA (Tate). 



"' Plate XCVII, figure 14. 



Orthisina compta Tate, 1892, Trans. Roy. Soc. South Australia, vol. 15, p. 185, PI. II, figs. 6 and 6a. (Described as 

 a new species. The specimen represented by figs. 6 and 6a is redrawn in this monograph, PL XCVII, fig. 14.) 



Form transversely subquadrilateral with the hiage Hne a httle shorter .than the greatest 

 width of the shell. Surface of the shell marked by strong, concentric ridges of growth that 

 cause undulations of variable extent, also fine radiating, rounded, depressed ribs that are a 

 httle wider than the interstitial furrows. The outer surface is exfoliated, but the interior 

 lamellae of the shell show small, irregularly distributed nodes on the ribs that are considered 

 to be the bases of spines similar to those on the surface of Nisusia festinata (BiUings) (PI. C, 

 fig. 1) and N. alberta (Walcott) (PI. C, fig. 3c). 



The ventral valve is moderately convex with a low median fold. Area of medium width 

 and projecting slightly backward ; it is divided midway by a rather broad, triangular delthyrium 

 that is nearly covered by a convex deltidium; the area and delthyrium are marked by fine 

 transverse fines of growth. 



Length of valve from beak to incurve of median fold, 6 mm.; greatest width, 9 mm.; 

 length of lunge fine, 7 mm. 



Oiservations. — This species is represented in the collection before me by a single speci- 

 men. This appears to be a ventral valve, but, unlike the ventral valve of N. festinata (PI. C, 

 figs. 1, la-d), which has a median sinus, it has a median fold. The area and convex deltidium 

 are fike those of the ventral valve of N. festinata. The fine ribs and quadrate form distinguish 

 this species from other species of the genus. 



Formation and locality.— Middlq? Cambrian: (315 [Tate, 1892, p. 185]) Limestone at Curramulka, Yorke 

 Peninsula, South Australia. 



Nisusia festinata (Billings). 



Text figure 6, page 299; Plate C, figures 1, la-j, 2, 2a-c. 



Orfhidna festinata Billings, 1861, Geol. Survey Canada, Paleozoic Fossils, vol. 1, p. 10, figs. 11 and 12. (Described 



as a new species.) 

 Orthisina festinata Billings, 1861, Report on the Geology of Vermont, vol. 2, p. 949, figs. 350-352. (Text and figures 



copied from preceding reference.). 

 Orthisina festinata Billings, 1862, Am. Jour. Sci., 2d ser., vol. 33, p. 105. (Discussed.) 

 Orthisina festinata Billings, 1862, Report on the Economic Geology of Vermont, by Hager, p. 221, figs. 350-352. (Text 



and figures copied from BUlings, 1861b, p. 10, figs. 11 and 12.) 

 Orthisina festinata Billings, 1863, Geol. Survey Canada, Fifteenth Rept. Progress, figs. 289a-c, p. 284. (No text 



reference. The figures are copied from Billings, 1861b, figs. 11 and 12, p. 10.) 

 Orthisina festinata Billings, Walcott, 1886, Bull. U. S. Geol. Survey No. 30, pp. 120-121, PI. VII, figs. 7, 7a-b. 



(Original description, Billings, 1861b, p. 10, copied. The two specimens represented by figs. 7 and 7a-b are 



redrawn in this monograph, PL C, figs, la and Ih, respectively.) 

 Orthisina festinata Billings, Walcott, 1891, Tenth Ann. Rept. U. S. Geol. Survey, p. 613, PL LXXII, figs. 7, 7a-b. 



(Mentioned. The figures are copied from the preceding reference.) 

 Billingsella festinata (Billings), Hall and Clakke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 230. 



(Merely changes generic reference.) 

 Nisusia festinata (Billings), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 249-251. (Described and discussed 



essentially as on p. 728.) 

 Nistisia festinata (Billings), Grabau and Shimek, 1907, North American Index Fossils, vol. 1, p. 211, fig. 249, p. 210. 



(Described. Fig. 249 is copied from Walcott, 1886b, PL VII, figs. 7, 7a-b.) 



