CAMBRIAN CRACHIOPODA WALCOTT 6l 



Genus OBOLUS Eichwald [1829, p. 274] 

 OBOLUS MEMBRANACEOUS, new species 



Plate 7, Figure ii 



In size and outline this species is somewhat similar to OboJiis 

 fcistniantcU (Barrande) [1879, pl- lo^* ^gs- iv: i-HJ p'- iio< %s. 

 \iii : 1-4]. but in its very thin, almost membranaceous shell it differs 

 from that species and all other species of the genus known to me. 

 Seven specimens w'ere collected from a shaly, compact limestone, all 

 as casts. Remnants of the corneous shell are preserved which show 

 it to have been very thin, and the interior casts show that it did not 

 retain any impressions of the animal sufficiently strong to be im- 

 pressed on the cast. A short, rather narrow cardinal area occurs 

 on both the ventral and dorsal valves. Outer surface smooth, with 

 a few lines of growth. The largest ventral valve has a length of 

 17 mm., with a width of 22 mm. A less distorted dorsal valve has 

 the same length and width, 15 mm. 



FoRMATiox AND LOCALITY. — Middle Cambrian: 4,250 feet (1295..1 

 m.) above the top of the Lower Cambrian and 860 feet (262.1 m.) 

 below the Upper Cambrian, in shales of the Eldon formation [Wal- 

 cott, 1908a, p. 3], at the north end of the amphitheater northwest of 

 IMount Bosworth. on the Continental Divide, north of the Canadian 

 Pacific Railway, British Columbia, Canada. 



OBOLUS PARVUS, new species 



Pl.\te 7, Figures 10 axd loa 



Shell small, rarely over 2.5 mm. in diameter, moderately convex, 

 nearly semicircular in outline. Ventral valve a little longer than 

 wide and with the umbo curving gently to the minute marginal beak. 

 Dorsal valve a little wider than long and wdth apex marginal. Sur- 

 face marked by minute concentric stride of growth and an exceed- 

 ingly fine network of irregular lines, that, with a lens magnifving 20 

 diameters, gives it the appearance of the surface of Liiigiilclla 

 (Liiigulcpis) long-iijcrz'is (^Matthew) [1903, p. 133]. Nothing is 

 known of the interior of the valves. 



Observations. — This small shell occurs in great abundance with 

 Micromitra (Patcriiia) zvapta (see p. 59), WimancUa simplex (see 

 p. ioi),AlbcrtcUa Jiclcna Walcott [1908^, p. 19], and other fossils of 

 the fauna of the upper portion of the Lower Cambrian terrane in 

 the Canadian Rocky ^Mountains. In form it resembles Obolus iiiiiii- 



